user's group order

Hi,

I have added 2 very-simple features:

One function in PermissionManager to get all groups for one user.
I have made this because JSONAPI do this with a very dirty way (get all player.dat -> get the group for each of them)

I have ordered user's groups with the same order as in the file. This is a workaround for this case:
group admin
group vip (inherit player)
group player

my admin can be admin+vip or admin+player but i always want their prefix to be admin. this function use the order of the group in the file