Options - Memory & Threads inaccurate

When you launch IJ2 when no ImageJ.cfg file exists (or no memory constraint exists within it) the dialog shows 256 mb. But the actual ram allocated might differ substantially depending upon how IJ2 was launched. Have the dialog default to the currently allocated number of megabytes. Also warn user that memory setting won't apply if they launched IJ2 by some method other than the launcher. We can detect this state via lookup of the property ij.executable that the launcher sets.

Migrated-From: http://trac.imagej.net/ticket/1089

Start by locating the Options - Memory & Threads dialog and the launcher handling of the ij.executable property. Check how the currently allocated megabytes are obtained, then verify that the dialog reflects that value and warns when the launcher was not used.

Written by the indexing model from the issue text.