RFC for Issue #256 Pluggable Components

A naive yet effective approach to disabling pluggable components:
* Do not load modules that have a special "comp_disable" file in their folder
* Allow associating right_bar items with components

Advantages
* Simplicity
* Minimal changes to the code repository on disabling a component

Disadvantages:
* Removing a right_bar item requires associating the "break" item as well
* Too simplistic - core components cannot really be removed