Enable tab navigation in forms.

Enable tab navigation in forms.

Implemented a TabNavigationListBox
that can be used when tab navigation is
required.

Also fixed views' status messages.

Tests: `make check`.

QA: start the demo app 
(`make` and `./cli-app-demo.py).
Use it to edit existing environments and
to create new ones (ec2 and local).
Check that the status messages make sense.
In the creation/edit forms you should
be able to navigate through the form fields
using tab and shift+tab.

https://code.launchpad.net/~frankban/juju-quickstart/tab-navigation/+merge/200403

(do not edit description out of merge proposal)

[frankban, 2014-01-03 14:22:07]

Please take a look.

[bac, 2014-01-03 14:43:55]

LGTM and QA is good, though I was surprised tab doesn't work between
save/cancel/restore, though you say it is a known limitation.

[frankban, 2014-01-03 14:46:23]

*** Submitted:

Enable tab navigation in forms.

Implemented a TabNavigationListBox
that can be used when tab navigation is
required.

Also fixed views' status messages.

Tests: `make check`.

QA: start the demo app 
(`make` and `./cli-app-demo.py).
Use it to edit existing environments and
to create new ones (ec2 and local).
Check that the status messages make sense.
In the creation/edit forms you should
be able to navigate through the form fields
using tab and shift+tab.

R=bac
CC=
https://codereview.appspot.com/47350044

[frankban, 2014-01-03 14:51:29]

Thank you!