Utilize placeholders and defaults for form entry

* RESOLVE michael-cannon/testimonials-widget#87 Fields placeholder attributes
* Utilize placeholders and defaults for testimonials form population
Merge commit '947036963d9b86250006a93a6f05d544494c1578' into 3.0.0RC2
Merge commit '82358047aa57957b01747c4ceeb9243d20fc37d3' into 3.0.0RC2
Limit characters on form entry

* RESOLVE michael-cannon/testimonials-widget#81 Form: Limit the number of characters a person can enter for the summary