Adding possibility to customise notifications sounds

[NeoHuncho]

I propose adding a feature for customizable notification sounds. I have a custom build with custom notification sounds and it makes such a difference.

If there's no opposition or ongoing similar work, I'll start developing this feature next week and submit a PR when ready

[sekwah41]

No opposition, we need to change it from default windows sounds anyway ^.^

[sekwah41]

Ill assign it to you for now :)

[roldanjr]

I think it's related to these PRs #602 and #606

[sekwah41]

Yep these all relate though 602 is more related to changing the default sound for everyone