Get rid of all-insets-toggle and explain how to replace it with inset-forall.

Get rid of all-insets-toggle and explain how to replace it with inset-forall.

Change inset-forall so that screen is not repainted at each iteration, since this lead to very slow opeartion on large files. This is not a problem for current uses, but can potentially lead to crashes.

See ticket #6641 for more thoughts and possible solutions.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@34092 a592a061-630c-0410-9148-cb99ea01b6c8