Introduce "group" tokens?

[jchodera]

It would be useful if we could introduce the concept of "target groups", where target tokens could be registered as part of a "group" and ocores could be pointed at a "target group" instead of individual targets or the entire set of available targets.

This might have several uses:

• Creating target groups for individual laboratories, such that local cluster resources could be directed at laboratory projects
• Creating target groups for project themes (e.g. cancer, HIV, amyloidosis) so that donors could contribute to specific scientific themes they find most interesting
• Creating target groups for projects where supercomputing resources are allocated for a specific project could be directed at a group of targets within that project