Consider following LDAP search query example:

    (&(objectClass=Person)(|(uid=%s)(mail=%s)))

Right now on first login attempt Gogs will use the text supplied on login form
as the newly created user name. In example query above the text matches against
both e-mail or user name. So if user puts the e-mail then the new Gogs user
name will be e-mail which may be undesired.

Using optional user name attribute setting we can explicitly say we want Gogs
user name to be certain LDAP attribute eg. `uid`, so even user will use e-mail
to login 1st time, the new account will receive correct user name.

The hyperlink and the display name of the branch if the branch is in a folder or the branch name has '#'

This allows the admin to disable the version information about gogs and
go in use in the footer.

- copy link button: #1396, #1168, #1668,
- synxtax highlight: #1712, #1549, #1315, #670
- z-index: #1942

This moves the minimum key sizes into the config file, so that anyone
can modify the restrictions.

"Enable this to disable..." is needlessly confusing, simplify it by being
upfront that this setting disables the Gravatar fetching.