Let ffnb have a dynamic size

[marcelmbn]

Is your feature request related to a problem? Please describe.
Currently, src/setparam.f90 looks as follows for ffnb:

   !> GFN-FF manual setup of nb list via xcontrol
   !  allows a maximum of 164 atoms neighbors to be changed
   !  ffnb(42,i) stores the number of neighbors of atom i
   integer :: ffnb(42,164) = -1

Describe the solution you'd like
Dynamic allocation of the number of atoms for which the neighbour list should be adapted.

Additional context
Implementation should start here:

xtb/src/set_module.f90

Line 784 in 1779d8a

case('ffnb' ); call rdblock(env,set_ffnb, line,id,copy,err,ncount)