port agent API into v3 part1

This changeset only copies the v2 files into the appropriate v3
directories unchanged. The copy as-is will not be loaded by either
the v2 or v3 extension loaders. The second changeset will then
make the changes required for it to work as a v3 extension.

This is being tried in order to make reviewing of extension
porting easier as gerrit will display only what is actually
changed for v3 rather than entirely new files.

Partially implements: bp v3-api-extension-versioning

Change-Id: Ib7c489769d9b07797366be5920cc23ab2074a768
Merge "port agent API into v3 part1"