Task:     -
RevBy:    Thorbjorn
AutoTest: -

Details:  - Mismatch of kinds in editor and editor factory.

Details:
This patch makes use of system icons as a base
and draws overlay on top. This should blend a bit better
into the native icon theme.

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:  - To make it conform to naming convention.

Details:  in all pluginspecs.