Add Desktop notifications

[ginnyTheCat]

Description

This adds Desktop notification support.

(These screenshots are taken in GNOME. They will look different on Windows and macOS.)

This change will however not play a custom sound like element web does. The OS will play a generic notification sound on it's own. Adding this feature at a later date however wouldn't be difficult.

Currently Cinny does not ask for notification permission by default on first launch like element web does. The permission can be granted by going to settings > notifications > request permission. Personally I think the element approach is more intuitive for new users. If the maintainers are ok with Cinny asking for notification permission after the first login I am more than happy to add this.

Fixes #182

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Preview: https://61f417e0a83c150ef05c7d85--pr-cinny.netlify.app
⚠️ Do you trust the author of this PR? Maybe this build will steal your keys or give you malware. Exercise caution. Use test accounts.

[ajbura]

Personally I think the element approach is more intuitive for new users. If the maintainers are ok with Cinny asking for notification permission after the first login I am more than happy to add this.

I am ok with asking notification permission after login.

Also I am getting the following error with crash when opening notifications tab in settings in Safari:
undefined is not an object (evaluating 'window.Notification.permission')

[ginnyTheCat]

It should not crash in Safari now and asks for permission on startup.