Implement app password creation support for bitbucket

[guyzmo]

to avoid relying on user+password in the gitconfig (and make it more easily revokable just in case…)

[guyzmo]

good news, the latest bitbucket update introduced privatekey support. Now we just need to figure how to use the API with the key.

[guyzmo]

Looks like it's working the same way it is now, though you need 2FA enabled: https://blog.bitbucket.org/2016/06/06/app-passwords-bitbucket-cloud/ …

[guyzmo]

I'm adding to the plan to switch the bitbucket library to pybitbucket which is still maintained.