Settings UI cleanup.

Improved/completed numerous names and descriptions of settings
Categorized the settings by topic and put them on different tabs
Converted the syntax to the new and not deprecated PropertyDefinitions based ones.
Fix failing unit test
Some improvements guided by the PR comments
Simplify the external rule settings and the code which is reading them in.
Fixes also an issue in my tests, where the first value got ignored.
Add numbers to categories to get them displayed in the wanted order in the UI
Change the names of the setting properties as decided in the PR discussion.

Cleanup settings ui #212
Merge pull request #212 from wenns/cleanup_settings_ui

Cleanup settings ui