[transform] Group::move_handle() improvements

Group handles are only used for scaling of the group content.
The group position is supposed to be scale-invariant. With this
changes the handles behave as intended as long as there is no
rotation within the matrix.
In the rotation case the drawing might get skewed (acceptable
effect not specially handled elsewhere) and the size/position
of the group change (no idea how to properly avoid this yet).
[transform] account for group properties with drs import

previously the potential transformation matrix was simply ignored
[transform] handle matrix given to DrsRenderer::draw_object()

special handling for group objects:
 - for the render branch use DiaTransformRenderer, but not it's draw_object,
   to see all the children's draw_object ourself
 - for the object branch we rely on this draw_object being called so need
   to inline group_draw here
 - to maintain the correct transform build our own queue of matrices like
   the DiaTransformRenderer would do through it's draw_object
svg: activate viewBox interpretation again on import

Now it is also applied on non-root svg elements defining a local
viewport. It is only used if we are _not_ importing shapes,
restricting otherwise was a mistake when shape import was added.
With the current shape set it was triggered very seldom , because
there are only 14 out of >700 shapes defining width, height and
viewBox.
[transform] svg: fix PyDia::SvgRenderer::draw_object(..,matrix)

Reorder elements in matrix string representation and use it
to write the <g transform="matrix(...)"
svg: named color fixes (no more pango_color_parse())

 - get rid of pango_color_parse(), at least for green the color
   value is wrong, also the fallback was hiding bugs with the
   internal list of named colors
 - _svg_named_colors array needs to be sorted on the color name.
   The lookup of green failed because of grey being before green
 - move color name termination logic to be in use for
   svg_named_color() - names from style string might be terminated
   by [; ]
pdf-import: fix some transformations

Correct updateCTM should not go without saveState/restoreState.
Page distribution should consider original group position.
svg: support class list lookup for CSS

Some restructuring to reduce code duplication and another
loop over stuff already expensive ;)
svg: fix some text transform

Using matrix->yy directly was a bad idea cause it can be negative.
Now using transform_length(), which will probably stay until the
Dia Text object supports full matrix transform.
svg: improved viewBox interpretation

- respect the viewBox attribute including floats and
  typical SVG number separators
- improve round-trip by only using viewBox width and
  height to calculate the user scale