fix 2 minor bugs: GERBVIEW: Button "Erase all layers" not working, EESCHEMA: Plot to Clipboard: EDA_DRAW_FRAME::PrintPage() error

* Push schematic back annotation code down into the appropriate class.
* Minor improvements to back annotate file selection code and user prompt
  strings.
* Minor tool bar tool tip capitalization fixes.
* Change tool bar ID error from message dialog to a debug assert message.

* Add item clarification context menu to EESchema when multiple unresolved
  items are found at the current cross hair position.
* Add collector class SCH_COLLECTOR for supporting multiple item hit testing.
* Removed bit wise masked filtering from schematic item hit testing.
* Removed all old hit testing functions and methods scattered about the
  EESchema source code.
* Move terminal point test function into SCH_SCREEN object.
* Fixed bug in terminal point test when terminating a bus to a label.
* Define the < operator for sorting schematic items.
* Add area calculation method to EDA_Rect item.
* Add method for returning an item's bitmap for menu display purposes.
* Add method for returning an item's menu text for menu display purposes.
* Changed EDA_ITEMS container from boost::ptr_vector to std::vector.
* Factor coordinate string conversion code from EDA_DRAW_FRAME to function
  CoordinateToString().

F1.) Allows you to disable a component from the Netlist.  Useful for connectors etc.
To exclude a component from the Spice Netlist add [Spice_Netlist_Enabled] user FIELD set to: N

F2.) Allows you to adapt to simulation libraries that require the netlist node 
sequence to be in a different order. To reorder the component spice node sequence 
add [Spice_Node_Sequence] user FIELD and define sequence: 2,1,0  I am using 
LTSpice, but this holds true for any SPICE subcircuit.

Eeschema: fix a *very serious* bug in netlist generation: sometimes the netlist forgets pins for components having more than one part per package, in hierarchical designs.

Gerbview:   Added: read Excellon files created by Pcbnew. The full Excellon command set is not supported, but drill files created by Pcbnew are supported.

F1.) Allows you to disable a component from the Netlist. Useful for connectors etc.
To exclude a component from the Spice Netlist add [Spice_Netlist_Enabled] user FIELD set to: N

F2.) Allows you to adapt to simulation libraries that require the netlist node sequence to be in a different order.
To reorder the component spice node sequence add [Spice_Node_Sequence] user FIELD and define sequence: 2,1,0 I am using LTSpice, but this holds true for any SPICE subcircuit.

Note1: Patch maintains existing SpiceNetlister behavior as far as I can tell
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Updated Patch from Prior release:
New Changes consists of:
1.) Now allowing user to put in less Nodes then exist on the actual part.
2.) Now echoing Schematic Sheet Netlist components come from. This helps users segment the netlist in to understandable blocks of code that mimic the schematic sheets.
3.) Retested.