Implemented export view in cross-project and cross-language searches

Depending on the load/behavior we observe, we might want to consider
caching some views.

Fixes evernote/pootle#9.

Conflicts:
	pootle/apps/pootle_project/urls.py
	pootle/apps/pootle_project/views.py
	pootle/templates/editor/export_view.html