Linking to JIRA issues doesn't work when you customise the JIRA issue key format

Its possible to change the project key format in JIRA so it is not in the form [A-Z][A-Z]+.

When linking issues crucible first validates the issue key passed conforms to {{^[A-Z]

-\d+$}} which doesn't work if you use alpha numeric project keys.

We should either skip the validation altogether or provide an a way to change the format regex so it can work with customised JIRA project keys.