Fix some minor issues
Eeszchema: Minor fixes.
Code cleanup: remove m_Son member in EDA_ITEM which was never used.
update fp-lib-table to footprint library renaming efforts.
*) Switch to later environment variable expansion in fp-lib-table.
*) Save library nickname in APP so upon module editor re-entry last is re-used.
*) Fix bug editing fp-lib-table Description field.
Add a place-holder Description to fp-lib-table rows
Pcbnew: fix graphic item undo/redo bug.  (--fixes lp:1252264)

* Use std::swap for PCB_LINE_T items in SwapData().
* Use std::swap for PCB_MODULE_EDGE_T items in SwapData().
* Add assignment operator to EDGE_MODULE object.
* Move code from copy method to assignment operator.
* Minor coding policy fixes.