feature: disable postpone and skip buttons while shortcuts are disabled

[deltragon]

Description

Resolves #566.

This PR locks the Skip/Postpone button as well while the keyboard shortcuts are disabled.
It also greys out the buttons, and removes the hover style to signal that they are non-interactive.

[deltragon]

I've opened this as a draft because I am unsure about this.
I do think I slightly prefer this over the limitconsecutiveskipping plugin, personally.
However, as this is implemented right now, it will be enabled by default - together with limitconsecutiveskipping. That may be a bit much.
So maybe this should controlled by its own setting, separate from the keyboard shortcuts, and off by default.

[adventuretc]

I always viewed the disabled keyboard shortcuts for n seconds feature as a primarily self-control feature, and only secondarily to prevent accidental keystrokes, so, this PR should definitely be part of the program.

[deltragon]

Well, if others agree, I'm certainly open to merging this. Rebased and fixed the typos.

[archisman-panigrahi]

Please tell me what I should look for when I test this

[adventuretc]

The mouse shouldn't be able to click the skip and postpone button on the break screen until the seconds specified in the second-to-last setting in the Settings.

I personally use this patch and works well on my end.