Introduce Content Rules for uniform content restriction

This module is designed as a single point of configuration that will provide a
contract to uniformly effect editing interactions and the user interface in
cohesive way.
Correct typo and add missing PubSub dependency
Lint content-rules
Correct some typoes
Support block formatting key combos
Remove errant debugger statements
Improve function name and documentation
d̶i̶s̶s̶a̶l̶l̶o̶w̶e̶d̶ → disallowed
Ensure that content rules are applied to editables at creation

Also fixed:

 * Correct use of $.merge instead of $.extend
 * Prevent generating broken markup in applyRules()
 * Improve inline documentation
Correct typo
Merge pull request #1163 from alohaeditor/dev-unified-configuration

Introduce Content Rules for uniform content restriction