Trigger refactor

Objective: Simplify the registration and use of triggers

Changes:

* Renamed ve.Command to ve.Trigger
* Renamed command demo to trigger demo
* Removed language prefixing of triggers
* Generating trigger tooltips rather than hard-coding them in i18n
* Added documentation to clarify that only 'mac' and 'pc' are supported platforms, and how the default is chosen
* Simplified trigger registry's register command
* Updated trigger registrations

Change-Id: Ibab6ad5b5c86f24707f064967dc2119a81125392
Merge "Trigger refactor"