Show loading indicator while importing concept IDs

[chrisknoll]

Depends on #38 .

When importing a large concept ID list, there could be several hundred lookups against the service. The UI is still responsive and could allow the user to perform other actions while this operation is in progress (saving while importing would be bad!). Therefore, we need to have a 'working' indicator in place to hold the user off from interacting with the tool until the work is complete.