Compression level (rebased onto develop)



This is the same as gh-2387 but rebased onto develop.

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Set the compression level to high when the plane is greater than 512x512. This value can be modified in  the configuration file.
This should speed up the opening of large images that do not qualify for pyramid generation

To test:
 * Start insight with LAN selected
 * View an image with plane size greater than 512x512.
 * Check that the compression is set to High in the toolbar.

It can tested using 2kx2k.jpg image in ```test_images_good\jpeg```