[UPD] web_dialog_size: reduce rpc call to get config

After installing web_dialog_size and setup its parameter, there's
a slight delay where we can see the modal at its normal size and then
after a rpc to ir.config_parameter:get_web_dialog_size_config() the
modal is maximized.

This commit is to set a session value then use it to set initial dialog
size upfront without delay.

web_dialog_size/models/__init__.py

@@ -1 +1,2 @@
 from . import ir_config_parameter
+from . import ir_http