GitLab

- 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

Which nicely adds the occurrances to the search output window for
navigation.

Before it would use Courier on all platforms, which didn't always look
nice. Now it uses the configured text editor font.

The file paths are now also normal size, at least personally I don't see
why they should use a larger font.

page of its own now

This stuff was all over the place, a relic from before the editor
settings were unified. Now the initialization is only done in
TextEditorSettings.

Fixes the .pro file editor and the generic project files editor, which
before only used the font settings.

    Task:     180315
    RevBy:
    Details:

Many singletons have their own instance() method, in which case there is
no need to use ICore::instance() to get access to them.

replace ExtensionSystem::PluginManager::instance()->getObject<Core::ICore>() by Core::ICore::instance()

forward declaration is sufficient.

Details:  - Naming convention

Details:  - To make it conform to naming convention.