[IMP] qweb doc, tests

* document qweb based (mostly) on JS version
* convert JS qweb tests to (mostly) language-independent XML so they can be
  used for JS and Python implementations
* add some more tests (e.g. precedence between t-value and body in t-set)
* remove ``t-import``
* fix parity in foreach(dict) (and rename some variables to make array and
  object versions more similar)

doc/reference/javascript.rst

@@ -5,6 +5,9 @@ Javascript
 Widgets
 =======
 
+.. qweb integration: ``template`` is an (optional) automatically rendered
+   template
+
 RPC
 ===