public static void resynchronizeOrDeleteMapThemeFolder() {
        MapThemeFolderSynchronizer.requestResynchronization(MAP_THEMES_FOLDER.getFolder(), MAP_THEMES_INTERNAL_FOLDER, isThemeSynchronizationActive());
    }
Depending on whether map theme folder synchronization is currently turned off or on, this
method does two different things:
* if turned off: app-private local folder is safely deleted
* if turned on: folder is re-synced (every change in source folder is synced to target folder)
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In any case, this method will take care of thread syncrhonization e.g. when a sync is currently running then
this sync will first be aborted, and only after that either target folder is deleted (if sync=off) or sync is restarted (if sync=on)
<br>
Call this method whenever you feel that there might be a change in Map Theme files in
public folder. Sync will be done in background task and reports its progress via toasts
main/src/main/java/cgeo/geocaching/maps/mapsforge/v6/RenderThemeHelper.java