remove checker_type model and tests

When I removed checker_type from the database, I forgot to
remove the model and the tests. Here it goes.
fix json format for gem_infos controller
fix database by adding fields to gem_checker
add has_changed view and controller
update db schema

forgot to commit this after adding the fields for the gem_checker_results
model
remove the index for has_changed class since we are not using it
add field reference_md5sum to has_changed

this field will contain the md5sum used as reference for determining if
the gem has_changed.
create links to the different checker results
add view to has license model
remove test links from rails_apps index
add is_gpl_compatible view
remove vim backup file that I had commited by error
add views for is_latest_version, is_native, is_rubygems
add has security_alerts views