use html5 history API instead of hash

we've been using hash to load sketches without refreshing the page like this:

because

the url looks nicer, and
it may help with #100, to loading files by relative paths in methods like loadJSON('data.json'). If we the server gets a request from http://p5ide.herokuapp.com/editor/sketch/568d9514f60b940300d5f2fd/assets/myimage.jpg we could see that the request is for that particular project, and return the image associated with that project that has that name.

To accomplish this, we can incorporate the vue-router module which we have not started using yet (it may not have been finished when the project began): http://vuejs.github.io/vue-router/en/api/properties.html

As part of this, it might be good to revisit the url structure projects. There are currently a few ways to "view" projects.

/editor?sketch=projectID - editor window
/view?sketch=projectID - full page link to a saved project. Finds all the files related to the project, parses and builds the index.html page on the server-side.
/sketch/output.html - the iframe inside of /editor. All sketch code is injected client-side before (re)loading. Currently served static, but this may need to change (see https://github.com/therewasaguy/p5js-webIDE/issues/99). This is similar to /preview (below), but adds a script to send messages from the iframe's console to the virtual debugging console.
/preview - for "preview in new window". Gets all file data from local storage, so we haven't been storing the projectID in the url.

I think the last 2 paths would need to include projectID in order to load assets with relative path (https://github.com/therewasaguy/p5js-webIDE/issues/100#issuecomment-170285300)

So maybe these could be the paths: /editor/username/projectID /view/username/projectID /preview/projectID /frameview/projectID

I think it's faster for MongoDB to find projects by ID than by name, though name is obviously friendlier.

therewasaguy / p5js-webIDE