Generated Gemfile with pg as default database gem

Generate standard rails gemfile

### Why?
Because we need a custom Gemfile in our rails project

### What Changed
* Overwrite `def gemfile` method to use custom Gemfile template
* Generated a `database.yml` file and add it to gitignore
* Generated a `database.example.yml`
* Creates the database
* Rename `spec/features` -> `spec/lib`