customizer: squelch error when can't save Gist

BS3 commits: 8ca182876debea1eb28c983606267b2bf9aa585d
Replace $.fn.bind with $.fn.on in alert docs

BS3 commits: f6d1a733f58f76864a137fa1d26db358dc2e9460
remove remaining analytics
ix grammar in "Underlined text" example

BS3 commits: d56026d489fb8db66c2db6aa0d222f1a3fa9261f