Countdown Timer: Some small fixes and improvements

[puppable]

In order of commit:

• fc77cfef7348ba989d963c1656015292243f482a Replaces the alarm-like timeup alert with one faithfully modeled after a typical digital kitchen timer (which now follows volume/vibration settings)
• 25fcd733b071a39c855497a6dce68e41ba4045c6 Fixes a divide-by-zero error when setting the time to zero seconds. Has since been made somewhat superfluous by 1bd63df18078bb910c35acc4972a76dc405453cc no longer allowing that in the first place, but the additional hardening doesn't hurt.
• b967b6b7977507bd36b57a15c3ae5a1ce71c0238 Fixes the math for wrapping the hour/minute/second selection, allowing it to wrap in both directions.

Further details can be found in the description for each commit

[0w0mewo]

Hey there. The improved codes have applied to my repo. Thank you. (I was writing the app as a practice on learning C two years ago and I had never thought that there were others interested in the project.)

[xMasterX]

Thanks!

[puppable]

@0w0mewo Coincidentally, this was one of the apps I was using to familiarize myself with Flipper's API for writing a somewhat related app of my own. I've personally found the Flipper to be a great device for mundane little utility apps without having all the complexity of a phone, so having a timer app available has been a great addition for my purposes. Thank you as well :)