timer: Add button to increase a running timer with 1 minute
Rebase of !195 with a fix for this problem: !195 (3a443c6f, comment 1847834)
I also tweaked the tooltip text to be "Add 1 Minute" instead of "Add 1 min", which was abbreviating the word "minute" and didn't use header capitalization. I also squashed 3a443c6f into a single commit.
Closes #216