README: document GITLAB_HTTPS setting
added GITLAB_SSL_SELF_SIGNED configuration option
added gitlab.https nginx template for ssl support
nginx: use the gitlab.https config if https is enabled
perform http to https redirection with same hostname as the request
redirect to the correct port during a http to https redirection

Fixes http to https redirection when the default https port is not used
got the GITLAB_PORT

For example running the container like so:
```bash
docker run -i -t --rm \
-p 4443:443 -p 8080:80 -e "GITLAB_HTTPS=true" -e "GITLAB_PORT=4443" \
sameersbn/gitlab:latest
```

Will make sure you are redirected to https://localhost:4443 when you
access the application at http://localhost:8080
export port 443
renamed gitlab.https to gitlab.https.strict
added gitlab.https.permissive nginx template that will be used when you want to allow both http and https access
added GITLAB_HTTPS_ONLY configuration option
gitlab-shell: use http over localhost to talk to gitlab-ce api whenever possible
gitlab-shell: use default gitlab_url talk to gitlab-ce api when signed ssl certificates are used
renamed config option GITLAB_SSL_SELF_SIGNED to SSL_SELF_SIGNED
added SSL_CERTIFICATE_PATH configuration option to specify path of ssl certificate
configure ssl session cache
README: update reference links
added SSL_DHPARAM_PATH configuration option to specify path of dhparam.pem file.
README: document SSL support
README: fix typos
ssl: check if required files exist before enabling https support