z-surface restraints scripts

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Closes #834 by adding a new subcommand z-surface-restraints to the haddock3-restraints CLI.

haddock3-restraints z-surface-restraints
  --pdb my_structure.pdb
  --residues 1,2,3 7,8,9
  --spacing 20
  --x-size 200
  --y-size 200
  --z-padding 5
  --output my_Zrestraints

Selected residues sets (in the above example 1,2,3 and 7,8,9), will define two plans with x-dim --x-size and y-dim --y-size placing beads every --spacing angstroms. Also, corresponding restraints are generated, resulting in the generation of both:

a beads.pdb file containing the coordinates of the shape beads
a restraints.tbl file containing specific restraints to each plans.

A series of examples are also provided, in examples/docking-protein-surface

TODO LIST

[x] Generate bead plans
[x] Generate restraints to plans
[x] Have proper tests
[ ] Benchmark

haddocking / haddock3

z-surface restraints scripts #839