In addition to logging the last login date and IP address on the web
interface, store the time stamp and IP address of the last SSH login in
the database.

This simplifies user banning if one of the new SSH interface features,
such as the voting mechanism implemented in 7ee2fddc

 (git-serve: Add
support for (un-)voting, 2017-01-23), is abused.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>