[LanguageSystem] Implemented language system
[LanguageSystem] Added ability for neutral entries

* Fixed potential issue with creating and updating entries
[LanguageSystem] Added cache
[LanguageSystem] Implemented resetCache method
[LanguageSystem] Fixed languageID issues

* Added missing conversions between 0 and null for the neutral language
[LanguageSystem] Added two methods

* Added getValues method in AbstractLanguageEntryCache
* Added isNeutralValue in AbstractLanguageEntryCache
[LanguageSystem] WIP: Added todo
[LanguageSystem] Rewritten updateEntries method

* updateEntries method of editor class uses now delete-insert mechanism
* The old code was commented out
[LanguageSystem] Reverted previous commit

* updateEntries truly updates; delete, insert is used if 0 exists as key in data
* If data is updated for neutral language, delete the rest
[LangSystem] Fixed typo
Merge branch 'api/29' into dev
Implemented Version system.

Added:
* IVersion
* IVersionableDatabaseObject
* IVersionableDatabaseObjectEditor
* AbstractVersion
* AbstractVersionableDatabaseObject
* AbstractVersionableDatabaseObjectEditor
Improved SQL query for getVersion
Improved implementation
[VersionSystem] Unique versionID introduced

* previous versionID became versionNumber
* versionID is now primary key of version table
[General] Updated copyright & comments

* Added missing file comments
* Updated copyright
[VersionSystem] Added cache classes

* The VersionableDatabaseObject utilizes now new cache
Merge branch 'api/28' into dev