Add External Notifications Column

[kernelkind]

closes #364

[kernelkind]

external_notifs.mp4

progress

[robagreda]

@kernelkind do you think that for subscriber to someonelse's notifications we should implement something like this?

First you have to paste the npub, hex or nip05 and we recognize it and show a preview of the user selected, in that same box we add the subscribe button. The same box/card design is the one we will use for previews on hover of the user avatars so we reuse it.

Any thoughts?