[Redmine] plugin install/uninstall

# Installing a plugin

- For Redmine 1.x:

rake db:migrate_plugins RAILS_ENV=production

- For Redmine 2.x:

rake redmine:plugins:migrate RAILS_ENV=production

# Uninstalling a plugin

- For Redmine 1.x:

rake db:migrate:plugin NAME=plugin_name VERSION=0 RAILS_ENV=production

- For Redmine 2.x:

rake redmine:plugins:migrate NAME=plugin_name VERSION=0 RAILS_ENV=production