Add ExtendedCall to PLCObject as a replacement of RemoteExec and reflect it in eRPC interface.

ExtendedCall is a generic remote procedure call that runtime code can register to and that IDE extensions can call.
For example a fieldbus extension can use ExtendedCall to browse the fieldbus devices connected to the runtime.

Re-using elements with Inkscape clones (svg:use)
=================================================

Re-use of pages
---------------

Re-use of widgets
-----------------

Re-use of SVG elements in widgets
---------------------------------