Taginfo improvements

[bhousel]

for #3955
There is a lot going on here, so I'm rolling several changes into a PR. The goal here is to significantly reduce the number of taginfo lookups that iD is doing, as most of them are unnecessary and they're starting to degrade the server performance.

• Extend debounce wait time from 100ms to 750 500ms (because touch typists)
• Blacklist the top 100 keys with the most values from doing value queries for combo boxes (exception: opening_hours)
• Don't reset the taginfo cache when the user saves to OpenStreetMap. Data doesn't change often enough to need this.
• We are using debounce wrong. If we don't also debounce the cache lookup, an earlier uncached call will sneak through and get called anyway. (e.g. 1. user types 'name', 2. we have it cached and return results for 'name', 3. debounce asks taginfo for 'nam' anyway)
• Stop calling taginfo once we get a result with one hit. (e.g. if typing 'vie' returns 'vietnamese' as the only meaningful result, we don't need to also call taginfo for 'viet', 'vietn', etc.)

cc @joto

[runnabot]

Deployed iD-runnable/taginfo_improvements. View on Runnable.
_{From Runnable}