Remove apt-get cleanup from Dockerfile

Purging/cleaning packages using apt doesn't actually reduce image size, and only creates additional layers, which doesn't add any benefit to the overall image.
Merge pull request #294 from ecnahc515/patch-2

Remove apt-get cleanup from Dockerfile
actually use SshPort variable

SshPort is defined (SSH_PORT) but the value is not actually used (just compared to default port 22).
Merge pull request #335 from taziden/patch-1

actually use SshPort variable
Revert "actually use SshPort variable"
Merge pull request #338 from gogits/revert-335-patch-1

Revert "actually use SshPort variable"
Make sure, .ssh directory and authorized_keys file are kept at correct permissions
Corrected log message
Moved defer f.Close() up so there is no chance of returning without closing and handled an error on f.Chmod
Finish new collaboration page
Merge pull request #352 from DerDackel/ssh-permissions

Ensure correct permissions on .ssh and authorized_keys file
Mirror fix on #352
bug fixed
Merge branch 'dev' of github.com:gogits/gogs into dev
Finish new hooks list page
Finish new web hook pages
UI: Bare repository does not have visual link to settings page
Page: Manage social accounts
Feature: Social sign in
Finish new reset password, etc.