Improve performance and accuracy of new star check approach

[iProdigy]

Closes #87.

• Incorporates #88 (Cache property lookups for canLoadUser(String))
• Lookup usernames in cache in O(1) time by saving lowercase version (rather than O(n) of Iterable#find)
• Don't bother with requesting extra pages if we have already cached the username
• Don't request full last page if there are no extra watchers on the page
• Request all pages since the last grabbed page instead of just the last page (solves a rare edge case now that traffic has lowered)
• Don't allocate unneeded lists (some memory gain)

[tipsy]

Thanks, looks good!