GPII-1014: Replace the slider adjuster for cursor size with plus/minus text field adjuster

The bug report: http://issues.gpii.net/browse/GPII-1014

This pull request also upgraded the infusion library to be in sync with the latest master: https://github.com/fluid-project/infusion/
I copied it from https://github.com/cindyli/prefsEditors/blob/master/src/shared/adjusters/messages/de/textSize.json

Google translation shows "minus" as "minus" in Germany, but "plus" as "mehr", which means "more". I think we probably should follow what translation for textSize is to be in sync across.