Improve handling of remote objects

[olexandr-konovalov]

Implement the registry of remote objects defined on GAP SCSCP server and redesign the way how the server resolves OpenMath references (thanks to @ChrisJefferson for pointing out)

[olexandr-konovalov]

For now, I've put a restriction at 06cf21a

[olexandr-konovalov]

See also #22 suggesting to stop using TemporaryGlobalVarName.