Add application/x-tiddler-dictionary to the list of pseudo binary types

Without this change tiddler with content type `application/x-tiddler-dictionary` gets corrupted.
It seems that it is not enough to make TW5 work with TiddlyWeb since there are some other issues I experience (maybe not related) - eg. custom palette which has this content type do not load automatically unless I open that tiddler manually.

Am I missing something?