expose unicorn timeout

Mitigate https://github.com/gitlabhq/gitlabhq/issues/1527
README: document UNICORN_TIMEOUT setting
gitlab: indentation fix
README: moved Upgrade instructions to bottom of the README
smtp: allow smtp configuration for mail delivery
README: document the available SMTP options.
README: added mail configuration section
README: add SMTP setting in the "Putting it all together section
README: updated references
Merge branch 'feature/smtp-support'

SMTP configuration can now be provided for email support.
README: moved "Other options" section to bottom of the page.
gitlab: renamed script parameter start -> app:start
gitlab: add db operation commands the app:db: prefix
gitlab: add help command the app: prefix
gitlab: align help text
Merge branch 'feature/cli-reborn'
gitlab: added the capability to run any installed *nix command

eg.
docker run -i -t sameersbn/gitlab top -d1
docker run -i -t sameersbn/gitlab /bin/bash -i
...and so on.
gitlab: exposed GITLAB_SIGNUP parameter to enable/disable user signup.
README: document GITLAB_SIGNUP setting
Merge branch 'feature/signups'