extended eduzen-tagging-notes application model.

Model changes:
- added 'Last Modified at' and 'Created at' Timestamps to 'Resources'
- added extensive 'License' and 'Author'-Types to 'Resources'
- aggregated 'Web Resources' to 'Resources'

Pending:
- switching implementation of time-features to new model
- allowing adding license and web-page infos to resources via gui
- allow users to manipulate the tag-filter per item
- enable users to edit and delete tags in single-resource/detail view
- consolidate timestamps on application level

Note: You must reset your DB.

Testing continues.