Opening the preferences dialog is too slow

[olejorgenb]

On my admittedly not very beefy hardware, the dialog needs 3-5s to show. First invocation is somewhat slower than subsequent ones.

I looked briefly at the code, and ran the jrat profiler, but I don't see any single offender, so I assume that the initial run-time more or less is required.

The dialog is created from scratch each time though, and a lot of the work are initializations. (eg. generate valid keyboard keys)

Simply caching the dialog instance doesn't cause any fatal problems. This also has the nice side effect of remembering where you where in the dialog last time.

Complications occurs when settings are changed externally though. Eg. if I add a imagery offset bookmark, this does not show in the cached dialog.

I guess no-one is very motivated to solve a issue that's getting less and less serious, and is mostly annoying to new users? :) (I poke a lot in the preferences of new applications at least)

Depending on how many cases like the imagery offset there is, I don't think it should be too much work to fix. Not that fun though.

Ps: Sorry if this has been discussed. I only found https://josm.openstreetmap.de/ticket/3693 (not impressed with the track search so far..)