Was a bit confusing that a MakeStep was constructed by a
MakeBuildStepFactory and configured by a MakeBuildStepConfigWidget.

The MakeStep of the generic project manager was renamed to
GenericMakeStep.

Reviewed-by: Roberto Raggi

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.

The entered information isn't stored yet for now, though.