Speed up specs by not re-creating the dummy_app each time

We've removed the prerequisite of refreshing the dummy app from the :rspec task.
It should speed up local TDD.

To make this work in TravisCI, we've added a before-script line that creates the
dummy_app before running RSpec for real.
Remove Gemfile.lock and add .gitignore
Add webmock development_dependency for stubbing HTTP calls to the API
Load dradis_core earlier (./lib/dradis-osvdb.rb)
Put the API and Filters in the right module. Add some specs