Manage More GitLab Settings Through Parameters

This request implements two changes, both having to do with the puppet-gitlab module accepting more parameters to customize the GitLab installation:

* Accept a new parameter, gitlab_projects, for setting the default number of projects for users in the gitlab.yml configuration file
* Accept three new parameters for configuring SSL: gitlab_ssl, gitlab_ssl_cert, and gitlab_ssl_key.  These parameters are used to configure gitlab/gitlab.yml, gitlab-shell/config.yml, and /etc/nginx/conf.d/gitlab.conf

Before merging this request, I need two things:
* Any other parameters in the gitlab configuration files that we might consider pulling into parameters
* Feedback on the nginx configuration file: https://gist.github.com/atomaka/5800691
  * Does it work? (having someone locally test that as well)
  * Are settings general enough?

Once these topics are discussed, I'll finish preparing this pull request by updating with README changes and merging the latest master commits in.