Revert "Just some sanity testing, as well as some foundation work."

This reverts commit a46cb13b165b828f54668108951e649594257700.
Added code stubs and feature proposal document. See toggle-empty-chan-filter-proposal.txt for a quick draft of the code changes that needs to be implemented in order to support this new feature.

As of now, the ActionSheet menu item has been added, and it currently just displays an alert box telling the user that the feature has not yet been supported. This was done simply as a placeholder, and to establish that the chain of execution occurs as expected. For all practical purposes, this commit should be seen as a sanity test.