[XWIKI-3544] Cache component resources needed for flawless document caching
[XWIKI-3544] Skin extensions should be always aware of caching document, otherwise they won't work
[misc] Add licence headers
[XWIKI-3544] Add legacy support for Skin extensions + tests
Merge pull request #304 from DarkKnightCZ/XWIKI-3544

[XWIKI-3544] Fix rendering cache for on-demand extensions