Add the number of claimable items to the personal overview screen

[karelstriegel]

If the user is allowed to claim one or more items then the number of claimable items is added to the submenu text "funded" in the overview screens(2)

If possible only the number of items the user can actually claim should be indicated. Mean the ones that he can perform an action on.

[nico-ptrs]

This is blocked until #218 is implemented. Without it we would need to fetch the status of all the funded items from GitHub every time we load the list.