Switch to polymer 3

[jkomoros]

And update README and tooling to support

[jkomoros]

Also then make sure that boardgame-util serve and others check for build/bundled or whatever and serve from there. build.SimpleStaticServer should take an option on whether to use that folder if it exists or not.

And make sure that build static --prod works, because currently the polymer builder doesn't seem to work.

These were captured in #655 originally

[jkomoros]

Also note this error and fix will need to be used: https://github.com/PolymerElements/paper-swatch-picker/issues/36

[jkomoros]

Installing polymer-cli doesn't work correctly. See https://github.com/Polymer/polymer-cli/issues/836#issuecomment-320238380 for workaround

[jkomoros]

• [x] there's a problem with src/boardgame-board.html that's tripping up some of the conversion
• [x] boargame-token's memoization is tripping up the converter
• [x] Modulizer doesn't seem to catch all of the various entrypoints. Probably need to boardgame-util build static so we can run on that composed project. Note though that modulizer doesn't like linked files (unclear if it cares about linked directories). Will need a build.Static(copy bool) variant that copies static files.
• [x] When done running modulizer on tmp/ , copy over all copied files back over into server/static (files in directories are fine). Oddly modulizer is getting some children (e.g. BoardgameTictacToeCell, but it's skipping everything listed in fragments.html for some reason. https://github.com/Polymer/polymer-modulizer/issues/211 . Maybe it's because it knows that the code that loads the fragments expects them to be named that way? Maybe remove them from fragments to get them to convert, and then modify the handful of places that load them? Maybe have to have an entrypoint in bower.json that lists them explicitly https://github.com/Polymer/polymer-modulizer/issues/461 Or literally include them as literal inline imports in the viers.html that use importHref, then un-literalize them after the conversion
• [x] Run modulizer (on a branch) https://www.polymer-project.org/3.0/docs/upgrade
• [x] Currently boardgame-user's template pieces are broken (nodelist isn't there), WTF??? Perhaps there's a misbalanced tag in the template or something?
• [x] Need to do anything for GamePathMixin?
• [x] How to get polymerfire working?
• [x] get debuganimations (which exercises token) to work
• [x] Expand move forms don't work (use local storage that's not available in module)
• [x] Make boardgame-util serve use polymer serve for the static files
• [x] Make sure the changes to use firebase directly are working
• [x] Figure out how to support bare module specifiers: https://www.polymer-project.org/3.0/docs/es6
• [x] Keep iterating until the web app loads (currently the polyfills don't work)
• [x] After running modulizer successfully, 1) Do the post-conversion cleanup steps as listed in the upgrade docs, 2) copy over the modified files in tmp/ (which are primarily json) and delete tmp 3) un-staticify the imports in boardgame-app, boardgame-render-game, boardgame-render-player-info 4) Make sure that the dynamic imports in those places use the new style 5) generated inde.html seems to have messed up the script blocks and added moduleimports for some reason
• [x] Modularize games examples
• [x] Can I use html template's and sub-composing to do composing of boardgame-component templates more directly? https://www.polymer-project.org/3.0/docs/api/utils/html-tag
• [x] Make sure that boardgame-util build static works
• [x] replace separate PolymerElement, html imports in stub output and player-info examples with single import
• [x] merge back to master
• [x] print the big banner for serve after polymer does
• [x] verify tutorial and default output for stub clients work
• [x] Running boardgame-util serve from non root of boardgame fails (Oddly the 't' from tictactoe is swallowed). path.RelativizePath shouldn't use a literal LCP, but split on path separator and walk as many as match (check to ensure trailing slash too)
• [x] build.ensureBowerComponents should be ensureNodeModules
• [x] Make sure that boardgame-util stub works for client output. Just cheat and have escape sequences e.g. ({[[ and ]]}) that are converted to {{ and }} after the template is rendereed to get around awkward escaping issues
• [x] Make sure that all of the various readmes are correct for