Smarter handling of cached text
Not drawing a destroyed bitmap look nicer than a grey square.

Fixes #444
Implemented pre-loading of text
Used SoftReference in all caches now.
Small fix to prevent timing issues
Catalog now uses fragments correctly.
Rolled back usage of SoftReference.
Rolled back SoftReference-related changes
Merge branch 'performance' into fragment_stack
Clear textloader cache on low memory
Merge branch 'performance' into fragment_stack
Tweaked the scheduling of preloading and pagenumbers
Merge branch 'performance' into fragment_stack
Custom feeds are now also in a seperate fragment
Fixed IndexOutOfBounds on pre-loading
ActionBar title is now correctly updated when popping from the stack.
Updated version number