Fix bug in starting up DefaultLegacyService

Before, if you opened an image prior to opening the processing panel,
the old IJ stuff would be loaded prior to IJ2 stuff so you get an
error. Calling the static DefaultLegacyService.preinit() gets rid of
this error but it must be called before any opportunity for calling old
IJ stuff. So, it must be moved out of IJPluginUtility to the main class
of JEX.
Fix canceling of JEX_Filters

Added check to see if the function is canceled.
Fixed reference to static string constants

Changed hard code to static reference
Change R scripture reference to more standard library

'RWeka' is much less standard than 'foreign'