Add delete button to notifications

Created by: pR0Ps

This commit adds a delete buttons to new message notifications. The option is available in both single and multi-recipient notifications.

It also changes the size of the button icons (for Android versions that support them) to a more standard size (24dp).

The use case for this feature is for things like spam messages, 2FA codes, and other messages that don't matter anymore after they've been read (Ex: "your monthly bill is blah")