Bug 8107 - Disabled buttons not distinguishable from enabled buttons

Bug 8107 - Disabled buttons not distinguishable from enabled buttons

Add a "greyed-out" style for disabled buttons.

Having looked through the templates for examples of usage of this
I'm not convinced that we should really be showing disabled buttons.
I think in general it would be better to hide or show a button
based on whether the action is available.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
I agree, I think hiding or showing is better, but this patch is
harmless enough, until we want to go fixing our usage

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>