Minor update to add some small fixes and improvements.

Changelog:

• Added a small text at the bottom of the view area showing the page number in full-screen mode, or when the toolbar is disabled (and the menu option to disable it if the user doesn't want/like it)
• FIX: set "en" as the current locale if the one asked for didn't exist. It was loading it correctly but not saving it to the settings.
• FIX: generate the mime type of the page images correctly, although it didn't seem to matter :)