Use standard library style members of wxArrayString (and wxString) ...

... which will make it easier to change the types of those containers to
std::vectors of other string-like classes

for wxString,

IsEmpty => empty
Clear => clear
Alloc => reserve

for wxArrayString,

Count => size
GetCount => size
IsEmpty => empty
Add => push_back
Clear => clear
Empty => clear
Sort => std::sort (only with default comparator)
SetCount => resize
Last => back
Item => operator []
Alloc => reserve

src/Theme.cpp

@@ -486,7 +486,7 @@ void ThemeBase::RegisterImage( int &iIndex, const wxImage &Image, const wxString
    mBitmaps.push_back( wxBitmap( Image ) );
 #endif
 
-   mBitmapNames.Add( Name );
+   mBitmapNames.push_back( Name );
    mBitmapFlags.push_back( mFlow.mFlags );
    mFlow.mFlags &= ~resFlagSkip;
    iIndex = mBitmaps.size() - 1;
@@ -496,7 +496,7 @@ void ThemeBase::RegisterColour( int &iIndex, const wxColour &Clr, const wxString
 {
    wxASSERT( iIndex == -1 ); // Don't initialise same colour twice!
    mColours.push_back( Clr );
-   mColourNames.Add( Name );
+   mColourNames.push_back( Name );
    iIndex = mColours.size() - 1;
 }