Bug 957220, part 1: Move png2ico out of config/config.mk, r=Standard8

--HG--
rename : build/pypng/png.py => mail/app/png.py
rename : build/png2ico.py => mail/app/png2ico.py
Bug 957220, part 2: Stop using LOBJS in comm-central, r=Standard8
Bug 957220, part 3: Fix shell metacharacter quoting issues, r=Standard8
Bug 957220, part 4: Make the Windows installer work under mozilla-central, r=Standard8, a=me