u_milestones isn't specific to a prum

[sbillinge]

Current behavior:
u_milestones only lists milestones to edit on a per prum basis. l_milestones will list all milestones for everyone, or filtered by person and so on.

Desired behavior:
u_milestones has this same behavior as l_milestones and allows any available milestone to be edited.

Note:
since u_milestones requires a database to be specified, its behavior will be a bit different from l_milestones which loads milestones from all available databases that satisfy the filter. I don't think we want to change this behavior as u_milestone needs to know which database to update (though we should think about this). However, a message could be printed along hte lines of "if you don't see a milestone that you are expecting, it may be in a different database than {this_database} that is being searched here. Update the database field to search a different database"