refactoring: findbugs
fix #2054: Navigate options are different
Add restrictions documentation on favorite handling
fix #2312: not all hint pictures are shown

Only "jpg" and "jpeg" extensions were recognized. Other image extensions
can be used, so recognize "png" and "gif" as well.

The regexp could probably be extended to accept arbitrary names, but
there is a risk of treating some non-pictures as false positives.
Merge branch 'release' into upstream
Adapter in list cannot be null

If the adapter is null, then something is probably wrong with the way we
manipulate it.
Refactoring: do not use global variables for data passing

Also, there is no need to use a separate handler, runOnUiThread is
enough here as we only deal with a single message.
Fixes #2126 + #2231
Fixes #2126 + #2231

Added update calls for filter, footer and title to refresh handler
Merge branch 'release' into upstream

Conflicts:
	main/src/cgeo/geocaching/cgeocaches.java
fix #2313: bad entries in history search
fix #1737: do not try to open a null filename

The settings may initially contain a null filename.
fix #2316: race condition in LeastRecentlyUsedSet

removeAll() must be synchronized as well. Otherwise, the documentation
states that it uses a (unsynchronized) iterator to perform the removal,
which causes race conditions.
fix #2317: exception when backing up the phone

We do not need a cgeoapplication instance anymore when trying to perform
a backup.
Do not translate untranslatable strings
Merge branch 'release' into upstream
fix #2314: mapsforge errouts with no sdcard
Merge branch 'release' into upstream
close #2291: improve color markers in TB logbook