- clear up some Q_OS_LINUX vs. Q_OS_UNIX
- clear up Q_WS_* vs. Q_OS_* (relatively theoretical exercise)
- use proper #if-#else cascades instead of free-standing #ifs

Reviewed-by: dt

Reviewed-by: dt

Reviewed-by: dt

Reviewed-by: Daniel Molkentin

Reviewed-by: Daniel Molkentin

When an example is selected, help and the project are opened
in a split view. We try to read the xml file provided for
QtDemo to extract details about the examples provided. Will
try all available Qts, starting with the default version. Will
fail gracefully (provide a message and disable controls) if
examples or demos cannot be found. Will work if help is not
found, but show an error.

Manage Sessions replaces "Restore last session" (which can be done by clicking
the "(last session)" session anyway. Also, added a "Create New Project" button.
Ensured that the welcome screen is only as high as needed (will orient on the
amount of items in the contained treewidgets). Scrolling is still last resort.

Putting Help Filter settings into a GroupBox

Putting Docs settings into a GroupBox

pros:
- the non-webkit version is not castrated any more
- i18n should become simpler
  - but need to make the buttons non-labels for optimal results
- if we introduce delayed loading of the help plugin, we would get
  webkit loading out of the startup's critical path alltogether

cons:
- the page might be a bit harder to modify for some

Hopefully i didn't miss a plugin.

Fixes: Introduce a cpp settingspage containing file naming conventions (lower case and suffixes). Reorder VCS settings pages.

Task: 241959, 248085

RevBy: Optics/Naming checked by con
Details: Give IOptionPage an id() to differentiate from trName(). Make showOptionsDialog return a bool (applied) and give it an optional parent. Change Cpp and form class wizards, give them a Configure... button to change those settings.

RevBy: con

Task:     248199

Task:     -
RevBy:    Thorbjorn
AutoTest: -

in place
RevBy:   con

RevBy:    - dt

Task:     - none
RevBy:    - Thorbjoern
AutoTest: - compile
Details:  - remove font settings stuff, since we overwrite it in coreplugin