When an experimental quality profile is active, the stage panel does not show that it is experimental.
It is however shown on the quality drop-down menu in Custom mode.
This commit also fixes the untranslated (hardcoded) 'Experimental' string in the dropdown in Custom.
Fixes the issue reported in CURA-6118.
The file was splitted in several other files to improve readability.
There is a new folder called PrintSetupSelector where all those files
will be.
Contributes to CURA-5941.