Migrating virtual machine templates between sites

@mkasztelnik @bwilk here is the migration feature. It is correlated with https://github.com/dice-cyfronet/migration-worker Still testing if it works correctly.
Yeap. Please take a look that we have "section" there for csses specific only for concrete section. If it is specific than it should go there. 

If you will create it as new file please don't forget to add appropriate import into [application.scss](https://github.com/dice-cyfronet/atmosphere/blob/feature_migrating_virtual_machine_templates/app/assets/stylesheets/atmosphere/application.scss)