Button colours set on AssistantComposerForm

The color of ShowUnchecked and ShowConfirmed
buttons is set to light green when they are enabled,
and transparent when they are not.
Renamed AssistantComposerMainForm

to AssistantComposerForm.
AssistantComposerForm.SetSettingsAreSaved()
is now called after a save.
Also, MoritzForm1 now also calls
AssistantComposerForm.DiscardAnyChanges()
before it closes the form.