Disable suspend-frame keybinding

I never use and sometimes hit it on accident when use C-x z.
Generalize km/follow-gwene-link

Don't use anything gwene-specific to follow the last link of the
message, so I can use this on other messages that have the main link at
the bottom.
Use diminish to shorten mode line
Add functions to bury and unbury gnus
Stop gnus agent from asking to go online
Disable vc for git