Nexusformat

* Adds requirement for the `hdf5plugin` package in order to enable additional compression filters.

* Provides an option to store lock files in a directory designated by an environment variable or preference parameter.
* Creates `nxgetconfig` and `nxsetconfig` functions for handling parameters, such as default compression and memory limits. The older `get` and `set` functions are kept for backward compatibility.

* Adds a `transpose` function to NXdata. The syntax is like the NumPy and NXfield `transpose` functions, but the function also permutes the axes.
* The `nxsignal` property returns a NXfield if it is the sole member of a NXdata group, even if the `signal` attribute is not set.
* Adds `moment`, `mean`, `var`, and `std` functions to NXfields, using the array indices as the x-axis values.
* Fixes compatibility with Matplotlib v3.6.

* Adds `nxopen` as an alias to `nxload`, returning the NeXus file tree as a `NXroot` object.
* Adds context manager functions to the `NXroot` class. This allows the use of `with nxopen(...) as f:` to open NeXus files in a similar way to the standard Python `open` syntax. In this example, `f` is the `NXroot` group of the NeXus file.
* Allows `NXroot` objects to be sorted by their internal names.
* Allows `NXlink` objects to be equated when they share the same target.
* Fixes a bug when plotting 2D data with the 'tab10' color map.

* Allows a lock expiry time to be set, after which locks are considered stale and automatically cleared. This defaults to 8 hours.
* Adds new functions, `nxgetlockexpiry` and `nxsetlockexpiry` to query and set, respectively, lock expiry times
* Fixes an issue that sometimes prevented a new lock from acquired in nested contextual menus.
* Catches exceptions caused by the deletion of a NeXus file that has already been loaded.