Modified ModularVisual to check dimension of color, added reactive polygon test and added color to visuals and examples

Minor fix post rebase

Fixed spelling mistake

Added reactive ellipse tests
Changed coordinates of test visuals
Added reactive regular polygon tests
Fixed  regular polygon tests
Replaced color and border_color attributes as Color objects, added Color.is_blank() method
Minor fixes
Merge pull request #368 from mssurajkaiga/reactive-visual-tests

WIP: Reactive Visual tests and integration of Color with visuals
WIP: mplexporter / pyplot interface
FIX: Py3k
FIX: Quieter nose
FIX: Cleaner example [ci skip]
WIP: Some text support [ci skip]
FIX: Fix text
ENH: Add Markers [ci skip]
FIX: Fix text size [ci skip]
FIX: Fix image
FIX: Fix size [ci skip]
FIX: Fix coords
ENH: Better example [ci skip]
FIX: Blocking [ci skip]