[Contexts] Improved the abstraction of contexts by bundling label and type information within the context dictionary.  This allows abstract profiles and worklists to be generated (e.g. in the mobile plugin), etc.  Eventually we can remove a ton of redundant code for profiles in the main GUI as well.
[Code Cleanup/Contexts] Embedded type information in all context dictionaries.

[Code Cleanup/Contexts] Removed hardcoded '|date' in date-based context tokens.  Now that we have type information in the dictionary we can do this dynamically.
* [Contexts/Messages] The generic label for Message records now shows the sender email, ticket mask, and ticket subject.  Previously this just showed an unhelpful '(message)' placeholder.  The label is used in Virtual Attendants, the Web-API, and the mobile app.
* [Contexts/Activity Log] Activity Log contexts now provide actor_* and target_* placeholders.  These can be used in Virtual Attendant behaviors, snippets, and the Web-API.
* [Contexts/Activity Log] Activity Log contexts now provide a human-readable 'event' placeholder to describe the activity being logged.  This can be used in Virtual Attendant behaviors, snippets, and the Web-API.
* [Contexts/Workers] Worker contexts now provide 'is_disabled' and 'is_superuser' placeholders.  These can be used in Virtual Attendant behaviors, snippets, and the Web-API.
[Code Cleanup/Time Tracking] Removed a redundant time formatting function in time tracking contexts.  This now uses DevblocksPlatform::strSecsToString()
[Code Cleanup/Contexts] Implemented a label and type for the '_label' token on all contexts. This allows simple context link shortcuts to be established as profile properties.
6.5-dev checkpoint