Ship ucdn and use it by default

[behdad]

Currently, UCDN is only built and used as default if neither glib nor ICU are present. This is tricky for latest versions of Unicode, as many times the found glib / ICU don't support latest version of Unicode we support. That's the root cause of Marchen script working in 1.3.4 win32 bundle release but not in 1.4.0; in 1.3.4, for irrelevant reasons, glib was disabled, but it's enabled in 1.4.0.

#386

I'm going forward and making ucdn default-on and first-priority.