Split js framework into different types for different usage

[Hanks Zhang <zh...@gmail.com>]

Currently, both vue, rax and the legacy ".we" framework are all packaged
into the js framework, but for one Weex page could only be written in one
specific framework, it doesn't need both of them at once.

I think it's a good idea to split js framework into different pieces.
Distinguish vue and rax, whether compile ES6, and whether use polyfills.
It's more practical for native to manage dependencies and isolate contexts.

Another advantage is it's possible to use smaller js framework packages in
some scenario. Take the v0.22.5 for example, the size of js frameworks
could be:


​

To achieve this, the file structure and build scripts of js framework
should be adjusted.

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Best Regards, Hanks