Allow 'current context' to work in AppleScript when multiple contexts are enabled

Created a `currentContextAsString` method in `CPController`. This is called by `current context` in Applescript, and will either return the `currentContextPath` (the current behavior) or will join the active contexts into a big string.
The method uses the code from `updateMenuBarAndContextMenu`, and I refactored that method to call the new one.

Fixes #325, fixes #323