Extremely long class list prevents exiting QuPath

[petebankhead]

Bug report

Describe the bug
QuPath has major problems if the list of available classifications is too long.

See https://forum.image.sc/t/extremely-long-class-list-prevents-exiting-qupath/44381 for details.

Expected behavior
QuPath closes elegantly, and retrieves the class list when restarted.

Additional context
Presumably we hit the 8192 character limit of what can be stored in preferences.

Note that this also impacts byte arrays (since they use Base64 encoding).

Options include:

• Use the user directory instead (but this might not be set)
• Encode the preferences in a different way, e.g. across multiple entries if needed

[petebankhead]

A script like the following can be used to replicate the problem:

guiscript=true

def pathClasses = []
for (int i = 0; i < 500; i++) {
    pathClasses << getPathClass('Another class ' + i)
}

getQuPath().getAvailablePathClasses().clear()
getQuPath().getAvailablePathClasses().addAll(pathClasses)

[petebankhead]

The fix will only save classification lists to the preferences if they can fit. Otherwise, the classification list can still be retrieved from a project in the future - but won't be stored in the preferences.

[petebankhead]

Fixed in #635 - will be included in v0.3.0.