Migration guide for PSK1 -> PSK2

[timeu]

Although the recent blog post mentions some of the differences (https://www.polymer-project.org/1.0/blog/2016-08-18-polymer-starter-kit-or-polymer-cli) some questions are still somehow unclear (at least to me):

• app-theme.html removed. How can it be themed (related to #819)
• how to migrate some of the additional gulp tasks (i.e. babel, etc) to the new custom polymer-build (related https://github.com/Polymer/polymer-cli/issues/243). Relevant: https://github.com/PolymerElements/generator-polymer-init-custom-build
• How and where to include 3rd party scripts to be in line with the PRPL concept)
• How to use polymer serve when there is a transpliation step (i.e. babel). Currently I can only serve the everything as is or the bundled/unbundled version. How can I serve something intermediate (after transpilation but without minification or at least with source maps)

[robdodson]

Good question. I'm going to be doing some more cleanup over the next couple of weeks and I'll try to write up answers to all of these