Git: Offer SSH key generation (and copying of pubkey to clipboard) from the "add repo" view

[amberin]

• :heavy_check_mark: I have searched for existing issues that may be the same as or related to mine.

This simplifies the setup immensely for non-experts, and encourages good security practices.

Many other apps with SSH support have this functionality, so it should not be too hard to implement.

I will look into it, if I can find the time.

[amberin]

#963 solves this.