Fix dialog interaction with InsetMathRef (leftover from changed

Fix dialog interaction with InsetMathRef (leftover from changed
InsetCommandParams)

	* src/mathed/InsetMathCommand.[Ch]
	(CommandInset::createDialogStr): Move to InsetMathRef, since it is
	no longer generic.

	* src/mathed/MathFactory.C
	(createInsetMath_fromDialogStr): Use InsetCommandMailer instead of
	manual parsing. This ensures that the syntax is correct.

	* src/mathed/InsetMathRef.[Ch]
	(InsetMathRef::createDialogStr): Moved here from InsetMathCommand,
	but use InsetCommandMailer.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@17738 a592a061-630c-0410-9148-cb99ea01b6c8