feat: dynamic tray icon and tool tip

[aleung]

Show current timer status in tray icon and tool tip.

The status includes disabled and outside of working hours. If it's active, the tool tip shows "Next break in xx minutes".

Based on the idea from @pieterdd in #107 #108. Rather than using different icons to show every 10 percent, I simplified it to three: full / half-full / almost-empty and added two settings to switch the icon at configured minutes remaining.

My personal use case only cares whether the cup is almost empty. I decide if I should have a break in advance or continue the next task.

Verified on Windows. Linux should work as well. MacOS is not supported.

Implements #93 #126

[holocronweaver]

Is there a way to disable the dynamic icons? I personally don't want dynamic icons, just monochrome.

[aleung]

Is there a way to disable the dynamic icons? I personally don't want dynamic icons, just monochrome.

Set to 0 minutes remaining will disable them.