Unit tests and coding standards

Updates JS to accommodate both Gutenberg and the Classic editor. Also introduces unit tests and conforms to coding standards.

Fixes #2 (closed) Fixes #3 (closed)

languages/wp-revisions-control.pot

@@ -5,7 +5,7 @@ msgstr ""
 "Project-Id-Version: WP Revisions Control 1.3\n"
 "Report-Msgid-Bugs-To: "
 "https://wordpress.org/support/plugin/wp-revisions-control\n"
-"POT-Creation-Date: 2019-05-25 17:22:47+00:00\n"
+"POT-Creation-Date: 2019-05-26 17:40:54+00:00\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=utf-8\n"
 "Content-Transfer-Encoding: 8bit\n"
@@ -90,7 +90,7 @@ msgstr ""
 msgid "You are not allowed to edit this post."
 msgstr ""
 
-#: inc/class-wp-revisions-control.php:375
+#: inc/class-wp-revisions-control.php:392
 #. translators: 1. Number of removed revisions, already formatted for locale.
 msgid "Removed %1$s revisions associated with this post."
 msgstr ""