Proposal: Add option for ending cycles on the hour or half-hour

[heisencoder]

The proposal is to add an option to the Setting menu to automatically adjust the Focus duration such that the focus time plus the break time end on the nearest hour or half hour.

This is a useful feature when you have 30-minute meetings scheduled sporadically throughout the day and want to be able to start a Pomodoro cycle at any time, regardless of whether you have a meeting starting soon.

Basically, in this mode, you would specify a duration range (maybe a default of 10 minutes to 40 minutes), and the Focus time would be adjusted so that Focus + Break ends on the half hour.

The motivation behind this feature is that I feel like I need to often avoid starting a Pomodoro or be overly concerned about clock alignment, and will often lack focus during this period. If I could just start a Pomodoro at any time, then I could get started faster, and stay better aligned to the half-hour.

[heisencoder]

Current proof-of-concept here: https://github.com/heisencoder/marinara/commit/c4bca7e99f56ca2662a8896d17799fc0eab0a2d2#diff-aae58a8f5d9ad7b16e1bbb21077093c2f8e697e6b3a2a82aa488a0b14559cadc

Still need to do the work of adding this to the options page and adding a unit test, but wanted to start with this to gauge overall interest.

[heisencoder]

Note that there was a bug in my proof-of-concept in which the duration would go to zero on the second Focus phase.