Save operation

This is work in progress task for adding "save" operation into atmosphere. We agreed that "save" operation will only replace VMTs with new saved VM. It will not update information about AT `name`, `description`, `port_mapping_templates`, `endpoints`, `initial_configurations` and this information will be presented in the API doc.

Before it can be merged into master following actions need to be finished:

  - [x] VMT versioning
  - [x] migration adding version into VMT should fill this value with number 1 for all VMT managed by atmosphere
  - [x] Save action
  - [x] Remove VMT older than version
  - [x] Monitoring task sets correct version when VMT is a copy of another VMT (such situation occurs during VMT migration into different compute site)
  - [x] REST interface invoking Save action
  - [x] Save REST API documentation

Fixes #13 
Hold your horses - migration to other compute sites is not yet implemented so this PR cannot take it into account.

Additional we **NEED** to remove all VMT after new VMT is in `active` state. If we will not do this than we can have situation when the same Appliance Type started twice will have VMs with totally different application started.