Made several changes

* Place ID field on top of URI
* -none- -> ''
* getName() (Nickname) -> getName()
* Public Comment Field
* Let Website appear in Social Media Column
Contributor Refinements V4 (raw)
For slugs set the value not the attr
Showpublic -> Visibility
Respect visibility
Several Changes

* Fixed several Bugs
* Public Comment (for Contributors) can now be used for episodes only
* Made \Podlove\List_Table ready for tables in tabs
* Groups & Roles have their own column now
* Added Public Comment to [podlove-contributor-list]
* Replaced <thead> ([podlove-contributor-list]) with <caption>
* Changes description for "visibility" and Default Contributors
export contributors
export rest of contributor metadata
emptying tables now also resets auto_increment by default
fix namespace issues
import contributors and metadata
refactor import module: use importTable method
exporter: fix ampersand issue
do not export empty values
merge conflict
increment version for rc1
namespace fixes
namespace fixes
Migration
Made Homepage & G+ Link more feasible