ve.track: add topic-based analytic event subscription

Replace ve.trackRegisterHandler with two methods: ve.trackSubscribe and
ve.trackSubscribeAll. The former takes an additional string argument 'topic',
which specifies a string prefix on which to match event names. The callback is
only called on matching events. The latter, ve.trackSubscribeAll, binds a
handler to all track events, regardless of topic.

This patch simplifies argument-handling by eliminating variadic ve.track calls
in favor of a single object that encodes all event data. The loose coupling of
track event emitters and subscribers makes relying on unnamed positional
argument conventions brittle; property access works better.

Change-Id: I3b58ce0f48ad3c9b56fcaa9c2226cc79bbcd4051
Merge "ve.track: add topic-based analytic event subscription"