Status message + Backups + Multiple rule search + Better error support

* Added a status message to the lower right corner that notifies the user when content is being requested from Danbooru. It can be disabled under preferences.
* Added a backup feature under preferences.
* Custom tag borders now support the status metatag.
* Custom tag borders now support multiple matching rules for a single match. This basically means more complex "or/any" matches.
* Changed the XMLHttpRequest error message for non-Danbooru specific errors to a more generic message in order to support most (if not all) of them.

Still roughing out the text for custom borders and backups.