Fix digest string conversion

BigInteger ignores insignificant leading 0's, thus some files fail to verify.
Merge pull request #56 from ce-4/patch-1

Fix digest string conversion in the verify method of the Volume class
Merge pull request #57 from dliw/master

German translation
Small fixes in german translation
Fix typos in de translation
Merge pull request #58 from ce-4/patch-2

Small fixes in german translation
Add android.permission.READ_EXTERNAL_STORAGE permission
Check header sanity before reading metadata, show error message toast.

Dictionaries downloaded with command line tools may end up being html
(of error page for example) with .aar extension. Previously no checks
were made, attempt to load metadata was made, sometimes with random
huge value for metadata length which would crash the app with
OutOfMemoryError.
Implement 'Find' action - find text in article
bump version
Normalize white space: trim trailing whitespace, untabify, indent with 4 spaces
Normalize indentation
Clean up some warnings
Format DictionariesActivity source
Update doc: add 1.5.0 changes
Update doc: add 1.6.0 changes
Fix crash on return to article view activity
Display error message on failed dictionary open longer
Fix indentation
bump version