New functionality added: Bunches

Bunches are groups of users - we could name them fleets, groups, sets or anything like these. It's a primary expectation to enable users to form such groups, and to track members - where they are, when have we last seen them.

We only added basic functionality yet:
- we can form a new bunch,
- we can invite users to our bunch,
- we can join bunches if we have an invitation,
- we can query real time locations of our bunches.

Privileges are adaptable enough to handle such cases, like 'I'm creating a bunch for my employees, but I don't want to be viewable by them'; such functionalities of the web interface will be added soon.

Try it, position your bunches!