Migrate labels etc directly into MetaContext and MetaKeyDefinition

Squashed commit of the following:

commit 81b7960d5f792b27d0594860de84732870292d82
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 13:25:24 2014 +0200

    Update docu

commit 02065af20d207b1a1863ca20ceed7ec12b30fcc3
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 13:20:00 2014 +0200

    Update docs

commit 349a5610f134483b209894e67db5cfb0924514d0
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 13:12:36 2014 +0200

    ... fix

commit 81baa053b2b41acc2a7ed9e2d24d6dafbf0b34a3
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 12:38:33 2014 +0200

    ... fix

commit f611388c666269f2c918235e707583948b279cbe
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 12:19:02 2014 +0200

     ... fix

commit fc97304a0d487059329e80a0398e57db1e3598f1
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 12:11:27 2014 +0200

    ... fix meta context factory

commit dd3516cabd827f594edba3c6150cb13486bf59fd
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Apr 30 11:00:39 2014 +0200

    DB refactoring move labels ...
Refactoring meta_terms table