Moved launch commands to utils.ssh.

Fixed
=====

* Fixed a bug that resulted in jobs not being properly submitted
  if they uses long model names (names longer than 20 characters).

Moved
=====

* Moved launch commands from models.sumbissions to utils.ssh.
Added tag subcommand.

Added
=====

* Added a tag subcommand that manages model tags.
Merge branch 'master' of https://github.com/csdms/wmt