* Change all code references to pin sheet and sheet label to sheet pin to
more closely match the sheet pin object for improved code readability.
* Change menu and tool bar text from pin sheet to sheet pin for improved
user readability.
* Moved sheet pin place method to sheet pin object source file.
* Move last sheet pin stored state information into schematic frame object.
* Add Doxygen comments for the sheet pin editing methods.
* Change default build to enable wxDC zooming.
* Move sheet label find function into SCH_SCREEN object.
* Move draw screen items function into SCH_SCREEN object.
* Remove redundant page print method from SCH_EDIT_FRAME.
* Add method to hit test for all items in SCH_SCREEN.
* Add method for testing if junction is required in SCH_SCREEN.
* Fix Doxygen waring in help_common_strings.h