Add support for more than three screens.

The change relates to the commands "focus-screen" and "throw-screen". It allows that more than three screens can be configured.

Uses new "screens" variable in the configuration to define the number of screens.
Add new "screens" variable in the configuration to define the number of screens.
Add commands "focus-screen-4"/"throw-screen-4" on shortcut mod + q
Switch from int to NSInteger
Fix "screens" configuration fallback
Merge pull request #176 from joramhoefs/development

Development