Extension bulk editor should more gracefully handle failure

[allen]

When selecting multiple extensions to Enable them, if one fails then all others fail. For example Export Ensemble (top of the list) doesn't work on my MAMP so when I select that as well as others when Enabling, none of them enable.

[allen]

From Alistair:

Need to confirm this. Ideally, if an Extension fails to install/enable/whatever the rest should continue, but list of messages added to a page alert. Might need direction on UI.