Updates to latest JS/CSS files

Also modifies README to indicate that gumby.init is required, and removes unnecessary ui/gumby.fittext.js file.

Fittext was removed from Gumby in https://github.com/GumbyFramework/Gumby/commit/dc86e00872a4b48f88ddb7cf9eefd749254495df#diff-06699bde2de33f4a073f0a7630005857.