Nano-cat

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* Added the option to decorate a qd surface with more than one type of ligand.

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* Added the ``optional.core.allignment`` keyword for determining how
ligands should be alligned with the core.
Accepted values are ``"sphere"`` and ``"surface"``.
* https://github.com/nlesc-nano/CAT/pull/87:
Ensure that part of the core-surface is accounted for when rotating ligands.
* https://github.com/nlesc-nano/CAT/pull/85 & https://github.com/nlesc-nano/CAT/pull/86:
Issue a warning when atoms are too close when constructing QDs.
* https://github.com/nlesc-nano/CAT/pull/85 & https://github.com/nlesc-nano/CAT/pull/86:
Improved warning handling.

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* Moved the ``CAT.recipes`` module to Nano-CAT.
* Moved the ``CAT.attachment.qd_opt_ff`` module to Nano-CAT.
* Created the ``CAT.workflow.key_map module`` for storing aliases
for ``DataFrame()`` columns.
* Cleaned the modules in ``CAT.workflows``.
* Updated tests.

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* Moved ``test_distribute()`` to it's own module: ``CAT.attachment.distribution_utils``.
* Added the ``brute_uniform_idx()`` for creating uniform/clustered distributions
in a brute-force manner, *i.e.* by finding the global minimum/maximum within
the set of all valid atom combinations.
* Generalized the ``array_combinations()`` function, it now accepts any
array-like object and can generate combinations along any user-specified axis.
* Added the ``get_nearest_neighbors()`` function for finding the ``k``
nearest-neighbors within a molecule.
* Added a recipe for marking a (sub-)set of surface atoms:
``CAT.recipes.mark_surface()``.
* Added a recipe for dissociating specific sets of surface atoms:
``CAT.recipes.dissociate_surface()``.
* Update to the general structure of the ``CAT.recipes`` modules.
* Multiple minor documentation adjustments.

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* Changed the default value of the CP2K ``EI_SCALE14`` keyword from 0.0 to 1.0
(*i.e.* the CHARMM forcefield default).
* Renamed the CAT ``activation_strain.scale_elstat`` keyword to ``.el_scale14``.
* Renamed the CAT ``activation_strain.scale_lj`` keyword to ``.lj_scale14``.
* Added the CAT ``activation_strain.dump_csv`` keyword for writing the raw
potential energies to a set of .csv files.
* Added the CAT ``activation_strain.shift_cutoff`` keyword.
Sets the value of all non-bonded potential to zero at ``activation_strain.distance_upper_bound``.
* A number of consistency improvements to the Schemas.

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* Small optimization improvements to ``edge_dist()``.
* Moved a number of functions around in the CAT.utils module.
* Added the ``optional.qd.dissociate.lig_pairs`` keyword for the BDE workflow.