reorganize options page and patch a bunch of stuff
This pull request combines my patches from GH-6 and GH-11 with a reorganization of the options page, which looks like this:

Thanks for your consideration.
Thank you for the patches, @sunaku. I will take a look at them this weekend.
Thanks @taicki :smiley_cat:! I have added another commit to this branch to track the number of currently active timers in the Omnibox Timer toolbar icon's badge text.
Hi, @sunaku. Sorry about the delay.
I am preparing v0.5.0 including your changes. This release will include many UI improvements. Tracking all the changes in prepare_v0.5.0 branch.
https://github.com/taicki/omnibox-timer/commits/prepare_v0.5.0
Awesome! :+1: Thanks for merging. :shipit: