Added new drag hover and drop states.
Blacklist login and logout from being interpreted as a charm url.
Merge pull request #397 from jaycee/blacklist-login-logout

Blacklist login and logout from being interpreted as a charm url.
Merge pull request #391 from huwshimi/hover-states

Added new drag hover and drop states.

Added new drop states and highlighting when tokens are dragged over drop targets.

QA:
- drag two charms to the canvas
- open the machine view
- start dragging one of the units
- the 'Create new machine' should appear in the header with new styling
- hover the unit over the drop area
- the background should go grey
- drop the unit on the header and click create in the constraints form
- click on the 'new0' machine
- start dragging the second unit
- the 'Create new machine' and 'Create new container' headers' targets should appear
- the machine and container tokens should show the 'Add to machine new0' and 'Add to container Bare metal' respectively
- hovering the unit over the headers and tokens should turn them grey
- dropping the unit on a header or token should make the drop areas disappear
Implement the create container workflow.

No matter how the user enters the workflow, they should end up seeing
the form to select a container type and (optionally) constraints.