[ ] Spinner
[ ] Improve add comic dialog

[X] Add Language property to comics
[X] Comic Manager
[X] Properties comic dialog
[X] Improve the comic loaging stuff
[X] Remove Edit menu
[X] Improve welcome and error messages
[X] Save to disk the comics selected by the user
[X] Cache system
[X] Debug system
[X] Disable Comic -> properties when no comic selected
[X] Comic List: ellipsise
[X] Save a comic as PNG
[X] Move vfs errors from stdout to message_view
[X] Disable save a copy menu item when loading comics 
[X] Update sensitive of previous and next buttons
  [X] When moving in a comic (first and last)
  [X] On an error (it should be possible to move back)
