Spacing restored, refactoring

- Several constants and functions moved.



git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@980 ef8490bc-f317-4725-81ed-e95a9aca1bcf
Bugs fixed, features implemented, and more.

- Feature (Bug) #79 fixed. Additionally, "Invert smart scroll" now works the
same way in both double page mode and single page mode.
- Feature #75 implemented. The scrollable area is automatically expanded if
necessary.
- Semantics changed: "smart scroll percentage" and similar prefs for smart
scrolling are now interpreted as respective maximum amounts. (The GUI does not
yet reflect these changes!)
- Bug fix: Scrollbars now disappear if you close the current directory/archive.
- MainWindow.is_on_first_page(self) removed.
- MainWindow.update_viewport_position introduced.
- MainWindow._clear_main_area introduced.
- Refactoring (less clutter in event.py!)
- NORMAL_AXES and SWAPPED_AXES moved from scrolling.py to constants.py.



git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@981 ef8490bc-f317-4725-81ed-e95a9aca1bcf