New: Pen and Brush classes implemented in svgdevicecontext

-Added Pen and Brush classes to devicecontext.h, including m_currentPen and m_currentBrush objects before implementing stack.

-Removed corresponding variables from svgdevicecontext.h

-Changed mentions of "style" to "opacity" for clarity's sake.

-Changed all references in svgdevicecontext to deal with m_currentPen/Brush rather than separate colour/width/opacity members.
New: bboxdevicecontext uses Pen objects

-Changed refs to m_penWidth in DrawRoundedRectangle to penWidth

-Changed refs to m_penWidth throughout to m_currentPen(.getWidth())
New: pen/brush stacks implemented in devicecontext

-Changed m_currentPen to a stack of Pen objects, same with brush.

-Reverted change to bboxdc.h
Merge pull request #56 from DDMAL/fonts

Pen/Brush stacks