Also changes the avatar from a jpeg to a png, to allow for
transparent background. The indexed png is also smaller in size.

Note that at the moment the default avatar is only used when
the user requested a custom avatar and the custom avatar file
is not found (should never happen).

In the future the default avatar could be used as a default
return when by-mail avatar lookups fail too (both gravatar
and libravatar support passing a default)

- Update locale bindata

From https://godoc.org/crypto/tls#Config

    ServerName is used to verify the hostname on the returned
    certificates unless InsecureSkipVerify is given. It is also included
    in the client's handshake to support virtual hosting unless it is
    an IP address.

This is needed for certificate validation without InsecureSkipVerify.

* Do not write HTML in text/plain mail part

Fixes #2928

* Pass text/plain first, text/html second

* Do not send plain/text email if html2text failed (untested)

- Update language choose dropdown to fit more languages

When use builtin SSH server with concurrent operations, there are probabilities
One connection could use the command from another connections.

Fix this by set SSH_ORIGINAL_COMMAND for each command, not set in global scope.

Replace spaces with "%20" in "urlPrefix", before markdon processing.
The spaces were causing blackfriday (markdown processor) to behave
strange. This fixes #2545.

- Fix go-gogs-client#10
- Related to #809

Both are possible on explore and admin panel

Collaborators have write access as default, and can be changed via repository
collaboration settings page to change between read, write and admin.