RESOLVE Math captcha broken on back button use

* RESOLVE michael-cannon/testimonials-widget#141 Math captcha doesn't work when going back in history
Add sortable columns to edit page

* RESOLVE michael-cannon/testimonials-widget#25 Add sortable columns to edit page
Replace "Source" with "Author"
Merge commit '7d3ac1a293c903a9a558c709a03d4d5bdfa846ae' into 2.0.0RC4