Circumvent icon setting on Android

Apparently the Firefox on Android API doesn't support setIcon, so it
crashes basically the whole core functionality. So if we're on Android,
just skip that part. This fixes #22.

I don't have Android so I can't test this fix. Hopefully it works.

Release Hotfix 1.3.1

Creates an exception for when the timeout is set to 0 and pages are
insta-blocked, so that you can still change the settings and aren't
eternally "locked out." Changes apply, but timeout changes don't take
effect until the next day.

Release Version 1.3.0

Introduces the major new delay pages feature: Turn it on and set a time, and all
tabs going to a blacklisted page will be delayed for that amount of time before
allowing access to said page, and then starting the actual timer.
Also cleans up code to more efficient and correct versions of methods and
processes, and allows 0 minutes on the timeout, effectively always blocking
blacklisted sites.

Release Version 1.2.0

Fixed major bug where the hourglass would never expire. Added a
whitelist and corresponding capabilities. Remodeled the options page a
bit. Added feature of timeout changes taking effect immediately, and
timeout changes being allowed even when no time left on the hourglass,
if the timeout is being lowered.

Release Version 1.0.1

Relase version 1.0.0