fix some FindBugs warnings
Merge pull request #3435 from marco-dev/fixImageUtilsFindBugs

fix some FindBugs warnings
fix compile errors in ImageUtils
#3376: handle error in Android framework
Adding missing german translation
Corrected @NonNull annotations
Fixes #3440 slovak translation typo
Merge pull request #3437 from marco-dev/fixImageUtilsAnnotations

No more comments, merging.
Corrected @NonNull annotations
Implements stable keys for opencaching waypoints

additionally extend ex- and import (gpx) to also contain visited and
userdefined.
fixes #3348 - Direction to cache still displayed in lists although
deselected
Fix #3441, 'Visited' not saved for own waypoints

To disambiguate own waypoints in merge, generate a unique prefix on addition to the cache
refactor: upgrade to butterknife 4
refactoring: upgrade to commons collections 4.0
Fixes #3317, Lost translations due to import from crowdin