Clarify the names and descriptions of the feature types

[jyasskin]

... to try to direct developers to the right one more often.

Changes

to

The discussion on blink-api-owners-discuss was generally positive, with some future improvements identified.

This does not change the

description in features' metadata sections because that string comes from

chromium-dashboard/internals/processes.py

Lines 410 to 414 in 7f37bd7

	BLINK_FAST_TRACK_PROCESS = Process(
	'Existing feature implementation',
	'Description of blink fast track process', # Not used yet.
	'When to use it', # Not used yet.
	BLINK_FAST_TRACK_STAGES)

instead of the JS form definition.

[DanielRyanSmith]

I think a change like this, while not a complete solution, will go far in avoiding wrong choices for feature type in the future.

[jyasskin]

The discussion on blink-api-owners-discuss suggested a couple changes, which I've adopted. The "New or changed feature" vs "catches up" descriptions could do more to explain exactly what's different between those options, but I don't have time to figure that out before going on vacation, so I'm going to merge this for the incremental improvement, and come back to it in another PR.