Add nested blocks Handlebars test

This test is broken in Handlebars@1.0.0-rc.3 because of a regression,
but that regression is fixed in Handlebars@v1.0.10.
Update Handlebars importing script and wrappers

This updates the scripts which import Handlebars and the YUI wrappers to
prepare for importing Handlebars@v1.0.10.
Import Handlebars @ v1.0.10

Updates Handlebars to the latest published [to npm] version.

**Note:** `Handlebars.VERSION` still reports "1.0.0-rc.3".
Update Handlebars change history
Merge branch 'handlebars-v1.0.10' into dev-master
Build Handlebars @ v1.0.10