[Release][GMRES] don't copy the Krylov basis in the update method

The full krylov basis is copied in the call of the method update(),
working with a reference to the krylov basis reduced the peak amount of allocated memory
by a factor of about 1.7 and improves the runtime by 4%.

Steffen: Also constified all applicable function arguments as suggested
         by Christian.

Closes FS#1378