This moves EESchema DLIST structures to rtree. These changes are more
fundamental than the pcbnew changes from 9163ac543888c01d11d1877d7c1
and 961b22d60 as eeschema operations were more dependent on passing
drawing list references around with SCH_ITEM* objects.
This adds a few tests on:
* LIB_PART
* SCH_PIN
* SCH_SHEET
* SCH_SHEET_PATH
These tests exercise some of the basic code paths in these classes
and show some of the expected behaviours.
None of these tests are particularly ground-breaking, but they
provide a starting point to build out further tests, and to ensure
the already-covered behaviour is stable.
It does expose some places where SCH_SHEET could probably use const.
Jeff Young
Seth Hillbrand
John Beard