Introduce scene class

[jo-mueller]

Based on #515

This is a first stab at an ome-zarr-py implementation of the scene metadata/layout that will be part of 0.6. It follows closely and builds upon the design principles of the NgffMultiscales class that's introduced in #515 and mirrors the design of the NgffHCSPlate I propose in #570

TODOs:

• Add tests
• Add documentation on how to update/append scenes
• Keep track internally of underlying graph structures, i.e. in an nx.DiGraph instance?

[codecov]

Codecov Report

❌ Patch coverage is 33.99209% with 167 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.16%. Comparing base (9a96549) to head (711efec).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
ome_zarr/classes/scene.py	13.21%	151 Missing ⚠️
ome_zarr/classes/image.py	78.37%	16 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (9a96549) and HEAD (711efec). Click for more details.

HEAD has 14 uploads less than BASE

Flag	BASE (9a96549)	HEAD (711efec)
	20	6

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #583      +/-   ##
==========================================
- Coverage   86.67%   81.16%   -5.51%     
==========================================
  Files          16       17       +1     
  Lines        2319     2538     +219     
==========================================
+ Hits         2010     2060      +50     
- Misses        309      478     +169     

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[jo-mueller]

@kevinyamauchi ready for beta-testing, I would say. Still missing:

• OMEZarrImage needs another keyword to pass the axis_type (i.e., channel, displacement). Right now we infer these from the axes kwarg (i.e., czyx), but we 'll need more flexibility once Displacements are multiscales ngff-spec#145 is merged (displacements require axis type "displacement"
• coordinateTransformations/whatever are currently not parsed into the class on read, which might lead to trouble when building the scene graph and it includes coordinates or displacements
• waaaaay more testing

[jo-mueller]

Also: needs a rebase