Added plots module with orthographic and grid plots

[niksirbi]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
It would be nice to have some in-built plotting funcitons to help us get a quick overview of an image stack. Such overviews can be useful for quality control - i.e to select images to be included in the template and to inspect the consequences of various preprocessing steps. They can also be used for quickly inspecting the resulting templates.

What does this PR do?

Adds a new plots.py module with two public functions:

• plot_orthographic() - generates a figure with 4 subplots: 3 for each section (frontal, horizontal, sagittal), and 1 with a top view surface rendering (an attenuated max intensity projection).
• plot_grid() - plots multiple slices of a specific section (e.g. frontal) as a grid.

Here's how these plots look:

Both functions are "anatomically literate", as in the produced plots are labelled with anatomical axes, courtesy of the AnatomicalSpace class from brainglobe-space. The user needs to supply the image orientation to the plotting functions (default is "ASR") to the best of their knowledge. If they've misjudged the image orientation, the results will be obvious on the plots.

Apart from the two public functions, the new module also contains a bunch of small private utilities used by the 2 main functions.

How has this PR been tested?

Manually tested on the SWC rat data. No unit tests added yet.

Is this a breaking change?

No.

Does this PR require an update to the documentation?

In principle yes, but I haven't documented the new functions anywhere, yet. That said, extensive docstrings have been added.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality (unit & integration)
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[alessandrofelder]

Thanks - the plots look great!

Minor nitpicks to make docs slightly more precise and check I've understood things correctly. Please merge when you've considered the nitpicks.