Add implement WeApp by Scala.js

[kaiwu]

WeApp aka Wechat Mini Programs is a form of an application based on WeChat, the most popular App used in China.

Wikipedia
In January 2018, Wechat announced a record of 580,000 mini-programs in its feature

WeApp has its official development platform, which comprises Js, XML, CSS and it requires
a specific directory structure, they all fit nicely to Scala.js and SBT (sbt-web, sbt-less)

WeUI for Scala.js implements the WeUI demo, which demonstrates many of WeApp's calibers.
In the process, it is a solid PoC that WeApp can be developed with Scala.js and SBT

I can do a PR against libraries/skeletons.md if needed

[sjrd]

I can do a PR against libraries/skeletons.md if needed

Sounds good. :)