fix issue#4: run gems-status and insert data into the database

Created a new rake task called gems_status:run that runs gems-status and
imports data into the database. In order that to work, several changes
have been needed:

- add a config/application.yml file in order to set up the gmail
  credentials
- .gitignore: ignore the application.yml, otherwise the gmail
  credentialis would be in git, and ignore the temp directories created
by gems-status
- Gemfile* : update gems-status which has some changes needed by
  gems-status-web and add the debugger gem
- README.rdoc: update with information about gems-status
- add SourceRepo model/view/controller: this is needed by the
  gems-status
- add email to the user model
- add Gemfile* as examples
- add a rake task for importing source_repos from a yaml file so that we
  can reuse the yaml file we already have been using with the
gems-status
- filter the security alerts that are for previous versions or that have
  been marked as "Ignored" or "Refused". This is how the gems-status
work when creating a report. However, in the future we may want to
change this behaviour.
- add the possibility to edit the version_fix in the security_alerts in
  the view
add validations to the models

since we have the gems-status:run task that imports data, we better have
some validations in order to prevent corrupted data in the db