Allow customisation of Issue Collector labels

At present, Issues created via an Issue Collector will have the label "collector-${id}" added to an Issue. This is a unique link back to the collector that processed the request.

Suggestion:

• A unique hash is not intuitive for users to read, when they view the Issue and see the label. 
• Allow for customisation of the label so that unique text (such as something descriptive) can be used instead of a hash.