Allow custom talk times with a query parameter.

Adding "?t=10m" or "?t=400" to the end of the URL will give you a
different talk duration.
Remove "changing countdown time" from todo list.
Fix a bug handling an empty time parameter.

Putting in "?t=" on the end of the URL would set a zero talk time,
making the timer go red immediately, which probably isn't what you want.
Merge pull request #1 from fatbusinessman/duration

Allow custom talk times with a query parameter.