Fetch vendor dependencies

Don't check in Ember, Handlebars, and jQuery files. Fetch them when needed.
Clean up fetched files in `make realclean`. Ignore fetched vendor files.
Ember 1.0 build uses 1.0.1, not RC3
tests can specify a Handlebars version
Ember 1.0.1 tests use Handlebars 1.1.0
Test against Ember canary, jQuery 1.11, Handlebars 1.3