[manifest] Mark all fields which are extensions

Any fields which don't adhere to the W3C Manifest spec are marked
with "(extension)". This requires the addition of an extra field
for "name", which is supported in a non-standards-based way in
Android Crosswalk 1+ and Tizen Crosswalk 1-6, then in a standards-based
way for Tizen Crosswalk 7.