#51 key annotations for updated and new keys

[Wolfgang Moestl]

Every time a project is released there are usually some new keys to be translated. In big property files it is very cumbersome for translators to find out which keys they have to work on.

For a translators it would be very usefull to filter the tree to show only new or updated keys.

This could be done by annotating a key when it was changed in the default property file or in case of creating a brand new key.