[BUG #7767] qx.Mobile Selectbox.resetValue() throws ValidationError
* Special case handling for resetValue() when an empty string was passed. This resets the SelectBox to null or index: 0 according to the "nullable" flag.
* Added test cases.
[BUG #7779] making qx.Website artifacts version-string free

- can be re-enabled using the VERSION_STRING macro in .json files
- (.html files need to be adapted by hand)
[BUG #7779] adapting 'website' skeleton

- retain version strings in file names for script/ artefacts
- let api/, test/ scripts be version-free
- also: using local test/script/q.min.js for test/index.html
  (instead of outside ../script/q.js)
[BUG #7779] retain version tags in 'server' skeleton files
[BUG #7779] make component/server file names version-free

- also re-worked the config 'export' list
[BUG #7779] fixed clean, distclean for website and its skeleton
[BUG #7779] switched website tutorial to non-versioned lib
[BUG #7779] adapt Makefile.release

- apply version strings when creating download lib
  (for <vers>/framework/q-<vers>.min.js, etc.)
- create download zip archive with versioned file names
- (also eliminating unnecessary 'script/' subfolder in archive)
- expect non-versioned file names from repo
[BUG #7779] adapted 'todo' app to non-versioned libs
[BUG #7779] removed version-independent files from bumpqxversion.py
[BUG #7779] extracted the code for versionification into a make macro

- this is pure text replacement and works with shell vars
- as a by-product another macro that works only with make variables
  (currently not used)
* Added tests for NumberField.
* Minor API doc fix.
* Doc Mobile Showcase
[BUG #7779] removed version number from file names
[BUG #7779] removed version strings from 'server' test scripts
remove remaining console.warn calls

- Comment.parse() is now side effect-free
[BUG #7799] remove qx.Class dependency
Had to revert the previous commit ("remove remaining console.warn calls")

- as these are currently the only places where those config keys are honored
  (lint-check/warn-unknown-jsdoc-keys and lint-check/warn-jsdoc-key-syntax)

- to eventually remove this code, the call sides of Comment.parse() and
  Comment.parseNode() would need to handle those config keys and the logging
  of related errors
- to achieve this it should be placed in a dedicated function, like
  'Comment.log_jsdoc_errors(list_of_entries, log_options)'
- so that call sides don't have to duplicate this code (or even think about it)

- this reverts commit 2dcbf69bbcbae8e55c156deec57c8a42b1a6efee.
[BUG #7800] use the constructor of qxWeb instances as the context object
Update for Manual chapter: "Resolution".
[BUG #7803] SetSelection of qx.ui.mobile.form.SelectBox does not work
* Added check for incoming value of setSelection(). Method now validates if value is a valid number.
* Added test for this check.