Connection points are no longer referenced by index but by their id.
This was required as ODF specifies 4 standard connection points with
reserved ids from 0-3 and custom connection points with ids > 3.

When loading connection points they may have ids that do not relate
to their index, so things would go wrong when trying to create connections
saved to files.

A rather basic support for loading connection points was added along
with some supporting functions to check if a connection point exists or
to get a specific connection point position.