prepare subtree split for a standalone library

[craue]

This replaces #118. The idea is to keep everything in the bundle repo, but moving all files meant to be available for the library into a dedicated folder (which can then be used for a subtree split).

It still is a heavy BC break due to lots of namespace changes, so I'm not sure if it's worth it. I even tried replacing classes within the old namespaces by proxies, but that didn't work for all of them, so it's useless to do half-way.

The subtree split is available for testing - https://github.com/craue/CraueFormFlow - but don't rely on forward-only commits as the branch might be rewritten several times until this PR is eventually merged.

[coveralls]

Coverage increased (+0.03%) when pulling 28f6e7cef2e13b1238f5808b9c18c6a3ce58d0d8 on prepare-subtree-split-for-library-without-proxies into 1b5a46f66c7eb658b3de6ce34176b9c0d0e2b720 on master.

[craue]

@daFish: Do you still see a need for this?