Eliminate many assumptions in Pcbnew's library manager, pertaining to locality of libraries and

their type, by using the more abstract PLUGIN::Footprint*() functions.

This is an intermediate phase only, other changes will be necessary as library table support comes in.
Encapsulate usage of library path searching, since that will go away as library table support comes in.
Add FOOTPRINT_EDIT_FRAME::{get,set}LibPath() and FOOTPRINT_EDIT_FRAME::{get,set}LibNickName() functions
to provide this encapsulation.

common/basicframe.cpp

@@ -506,13 +506,6 @@ void EDA_BASE_FRAME::CopyVersionInfoToClipboard( wxCommandEvent&  event )
 
     tmp << wxT( "Options: " );
 
-    tmp << wxT( "USE_PCBNEW_SEXPR_FILE_FORMAT=" );
-#ifdef USE_PCBNEW_SEXPR_FILE_FORMAT
-    tmp << wxT( "ON\n" );
-#else
-    tmp << wxT( "OFF\n" );
-#endif
-
     tmp << wxT( "         USE_PCBNEW_NANOMETRES=" );
 #ifdef USE_PCBNEW_NANOMETRES
     tmp << wxT( "ON\n" );
@@ -520,13 +513,6 @@ void EDA_BASE_FRAME::CopyVersionInfoToClipboard( wxCommandEvent&  event )
     tmp << wxT( "OFF\n" );
 #endif
 
-    tmp << wxT( "         USE_PCBNEW_SEXPR_FOOTPRINT_LIBS=" );
-#ifdef USE_PCBNEW_SEXPR_FOOTPRINT_LIBS
-    tmp << wxT( "ON\n" );
-#else
-    tmp << wxT( "OFF\n" );
-#endif
-
     tmp << wxT( "         KICAD_GOST=" );
 #ifdef KICAD_GOST
     tmp << wxT( "ON\n" );