[Runtime] Add Manifest keys handler mechanism

The key handler can parse specific member in manifest.json for more
information, and save these information into the Application object, by
this, it will be easier to use without parsing these information every
time. The mechanism also can treat dependence relationship between
Manifest keys, it make sure that a high priority key will be always
parsed before a low one, means that when parsing the low priority key,
all required information has been prepared yet.

The key handler also can validate if the key value is allowed for this
application.

All keys handlers should be registered in
RegisterManifestHandlers().