Add notification .proto file.
Change protobuf message name.
Add callback registering.
Add service for receiving signal.
Add tests for registering signals.
Move symmetric encryption code to leap.soledad.
Add changes file.
Add possibility of unregistering in events mechanism.
Merge remote-tracking branch 'drebs/feature/2696-implement-unregister-in-events-2' into develop
Merge remote-tracking branch 'drebs/feature/2602-remove-soledad-strict-dependency-on-leap.common' into develop
Bugfix: use the provider's default language as default string

Also take care (and note) a possible case with a problematic provider
misconfiguration.
Merge remote-tracking branch 'ivan/bug/fix_default_language_localization' into develop
Fold in changes for 0.2.2
Merge branch 'master' into release-0.2.5
Merge branch 'release-0.2.5' into develop
Add tests for the BaseConfig class.
Merge remote-tracking branch 'ivan/feature/3030_baseconfig-tests' into develop
Improve leap_assert traceback logging
Add osx temp dir prefix
Merge remote-tracking branch 'chiiph/feature/improve_leap_assert' into develop