MyDash: update to 3.14.2 AppIcon upstream code.

This fixes #119 for gnome-shell 3.14.2
However this should break on previous versions
See https://bugzilla.gnome.org/show_bug.cgi?id=739497
MyDash: restore compatibility with 3.14 and 3.14.1 after previous commit.

This is a temporary workaround which can be dropped after transition to 3.16. I
just don't want to split the codebase for a point release.