* Add drag context menu entry for junctions that actually form a junction
with wires to EESchema.
* Add function to test for junctions to SCH_COLLECTOR class.
* Create annotate type and sort order enums to eliminate magic numbers
used in annotate code.
* Remove duplicate Doxygen comments from annotate.cpp and improve the
actual Doxygen comments in wxEeschemaStruct.h.
Eeschema: cleaning code. Start work to enhance annotation algorithm.
Already added an option to annotate using sheet number (sheet 1 uses numbers 100 to 199, sheet 2 uses 200 to 299..).
Works fine if deleting existing annotation, but needs work to be used when the existing annotation is kept .