internal/v4/api: added actions handling
Merge branch 'v4' of https://github.com/juju/charmstore into v4-actions

Conflicts:
	internal/v4/api.go
Merge branch 'v4' of https://github.com/juju/charmstore into v4-actions
* new version of charm actions implementation
* added charm actions test description
Merge pull request #40 from urosj/v4

internal/v4/api: added actions handling