Add simple progress bar to simulations

[viljarjf]

Description of the change

Adds a simple progress bar for simulations with SimulationGenerator

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black

Minimal example of the bug fix or new feature

from orix.quaternion import Rotation
from orix.crystal_map import Phase
from diffsims.generators.simulation_generator import SimulationGenerator
from diffpy.structure import Atom, Lattice, Structure

# Each phase gets its own progress bar
l = Lattice(1, 2, 3, 90, 100, 110)
atoms = [Atom("C", (0, 0, 0))]
s = Structure(atoms, l)
p1 = Phase("first phase", space_group=1, structure=s)
p2 = Phase("number 2", space_group=191, structure=s)

rots1 = Rotation.random(1000)
rots2 = Rotation.random(2000)

gen = SimulationGenerator()
sims = gen.calculate_diffraction2d(
    phase=[p1, p2],
    rotation=[rots1, rots2],
    show_progressbar=True,
)

>>> first phase: 100%|██████████| 1000/1000 [00:00<00:00, 2725.90it/s]
>>> number 2: 100%|██████████| 2000/2000 [00:01<00:00, 1909.23it/s]

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the
  unreleased section in CHANGELOG.rst.
• Contributor(s) are listed correctly in credits in diffsims/release_info.py and
  in .zenodo.json.

[pc494]

LGTM, will merge in a couple of days if nobody else reviews :)

[pc494]

@viljarjf I've just realised you aren't on the contributors list. I think you would go in above Isabel Wood. Similarly if you're happy to update the changelog that would be great :)