Few updates to .gitignore:

- excluded files created by Symbian in-source builds;
- excluded files created by Harmattan in-source builds;
- excluded moc, obj and rcc dirs which are forced by Qt Creator when
  building for Harmattan target.
Fixed few rules in the project file:

- instead of excluding all other possible platforms for Maemo/Harmattan
  booster, just test for Maemo/MeeGo;
- don't include/build mainwindow.* files when targeting Maemo/Harmattan.