Some tentative changes to the translations panel, based on suggestions
Denisa made. Specifically:
-Translations processing can now be paused and resumed
-The user should be able to swap in a sentence while translations are
proccessing without crashes/other issues
-Each sentence will now have its own translator thread, as switching
from sentence to sentence while pausing/resuming translations was too
complicated with a single shared thread
-The colors that indicate the quality of the translations now reflect
whether the translation increases or decreases anonymity. Translations
that increase anonymity will always be more green than red and
translations that decrease anonymity will always be more read than
green, with intensity based on the ordering as before.

There are still several bugs, so these changes are probably not final.