[#BUG 7095] Table blocking mouse wheel even if empty
Tree controller now assigns node after tree is built.

This is a great way to use the changeRoot event as a trigger for things
that need to happen when the tree is available, like opening nodes.
[BUG #6968] minor config
fix typo (s/unelectable/unselectable/)
[BUG #7332] add rest samples file
[BUG #6674] make ContribLoader work with contrib-catalog repo

- retained old code as ContribLoader_1
[BUG #6674] use the checksum to validate the archive
qx.Mobile documentation update
fixed api warning
[BUG #7418] Do not apply the keep frame if the animation has been stopped before end.
[BUG #7097] refine global error handling usage
[BUG #7279] reliable compile warnings slow down build of framework apps

- esp. 'test', 'api' jobs
- where all the qx.* classes are 'application classes'
- hence pot. lint warnings are retrieved from the classCache
  (-> disk IO?!)
[BUG #6674] add dedicated contrib page to manual
Removed typo
Moved env key declaration to inspector.json to prevent warning in source version
removed old PDF-based generator cheat sheets

- there is a current one as a normal manual page
  (pages/tool/generator/cheat_sheet.rst)
- easier to maintain, can still be selectively printed
- it just doesn't have the compact format
[BUG #6674] adapted to new 'contributions' subdir in catalog
[BUG #7292] patch query param retrieval to always lowercase search words
[BUG #7292] patch word regex to also permit words with dots or hyphens
[BUG #6674] add http(s) support to 'manifest' config entries

- url has either to end in '.json', for a catalog entry, or '.zip/.tar.gz/...',
  for an downloadable archive
- this also fixes bug#6044

- caveat: these changes can no longer be ported backwards to earlier qooxdoo versions,
  by just copying the latest ContribLoader.py to the older tool chain