Make line_iterator less slow
Don't overwrite alpha when using the color picker screen dropper
Add tool to repack thesaurus dictionaries

The standard MyThes dictionaries include words that we don't support
(nearly half the entries in the English dictionary have speaces in them)
which waste space, and they aren't UTF-8 which slows down loading as we
need to convert them.

Knocks a total of 10 MB off the thesaurus dictionaries.
Use a flat_map for the thesaurus index
Refactor thesaurus language listing a bit
Load the thesaurus dictionary asynchronously
Refactor spellchecker language listing
Explicitly link boost.chrono

Boost.thread sometimes fails to link without this.