OMEPyramidWriter ignores file extension to always write ome.tif

[petebankhead]

Bug report

Describe the bug
OMEPyramidWriter was created to write OME-TIFF images. However, it is possible to pass it a path with any extension - in which case it may write an ome.tif masquerading as something else.

To Reproduce
Steps to reproduce the behavior:

1. Open a 'small' image, e.g. CMU-1-Small-Region.svs
2. Run a script like the one below to try to write a JPEG 2000 image
3. Use tiff info to confirm that the .jp2 image written is actually a TIFF

import qupath.lib.images.writers.ome.OMEPyramidWriter
    OMEPyramidWriter.writeImage(getCurrentServer(),
    "/path/to/output.jp2",
    OMEPyramidWriter.CompressionType.J2K)

Expected behavior
There are three main options:

1. Refuse to write the image if it doesn't end with ome.tif
2. Add ome.tif as a file extension if it is originally anything else
3. Actually support writing in different file formats, if allowed by Bio-Formats

The third seems more desirable - particularly as Bio-Formats 6.8.0 introduces support for writing DICOM whole slide images, which may be very useful in the future.

Desktop (please complete the following information):

• OS: All
• QuPath Version 0.3.0

Additional context
I have explored some small changes that come closer to supporting different file formats, although there can be some gotchas - for example, if other formats don't support multiple resolutions or tiling, or require the reader to be initialised in a specific way.

It is likely that QuPath's OMEPyramidWriter.CompressionType may become inadequate; certainly it isn't desirable to always require a compression type for formats where it isn't customisable.