New method deleteGroups

- delete list of groups sorted by name (reverse) 
- use existing deleteGroup methods with force parameter
- add tests for this new method
- add method to RPC
Password manager with sample configuration.
Use native reverseComparation instead of multiplication by -1.
Merge pull request #288 from stavamichal/deleteGroups

New method deleteGroups

 - delete list of groups sorted by name (reverse)
 - use existing deleteGroup methods with force parameter
 - add tests for this new method
 - add method to RPC
UTILS: fixed typo

- fixed typo and format
Merge pull request #300 from zlamalp/typo

UTILS: fixed typo
GUI: implemented new way of deleting groups

- Delete list of groups instead of single groups.
  This will ensure, that delete is performed in right order and
  uses 1 single call to core instead of multiple.