Replace testimonials_widget_ with tw_

* RESOLVE michael-cannon/testimonials-widget#113 Replace testimonials_widget_ of actions, filters, and functions with tw_
Merge commit 'f476dcf0a440bf3df8d0fd9e277c7270ff9d74f5' into 2.0.0RC1

* Restore Testimonials Widget branding
* Restore Testimonials Widget Premium branding

Conflicts:
	includes/libraries/testimonials-widget/API.md
	includes/libraries/testimonials-widget/CHANGELOG.md
	includes/libraries/testimonials-widget/includes/class-testimonials-widget-settings.php
Merge commit 'dd8fb5473c0a5fff2fa1917b90a8f66906236a0c' into 2.0.0RC1
Merge commit '643963b09b6809135cd0716af4e1bc53d6dd8b12' into 2.0.0RC1
Merge commit 'a739b432ed92e68ca21a5edc25be9b434b64c644' into 2.0.0RC1
Merge commit '62b4b4ddb6efba7267bdd2a2409fb21326e3371c' into 2.0.0RC1
Initial TW 3.0.0RC1 pull
Adapt for TW 3.0.0RC1

* Don't show donation or premium upgrade links by default
* Removed filter `twp_next_text`
* RESOLVE michael-cannon/testimonials-widget#103 Example of every option
* RESOLVE michael-cannon/testimonials-widget#107 Make text labels easier to replace
* RESOLVE michael-cannon/testimonials-widget#109 Open full testimonial in a lightbox #109
* RESOLVE michael-cannon/testimonials-widget#123 Revise installation and usage instructions for ease of use
* RESOLVE michael-cannon/testimonials-widget#19 Template engine