Add Vector testing template to Agora

This is just an empty Vector page for testing Agora elements in
a real-world (e.g. non-CodePen, non-JSFiddle, etc.) environment.

Test pages for all existing elements are forthcoming.

Patch 2:
- Dropped leading underscore from filenames
- Exported template dependencies in unminified state

Change-Id: I7c22735e5b70bfbb7ce3b770950fb4f8a0c21cbc
Merge "Add Vector testing template to Agora"