Merge pull request #12 from jlewin/development

Adjust assembly loading mechanism for plugins on Android
Made the rest of the plugin code have the right #if
Made scroll widget able to scroll on click and drag.
Make the interface match
Merge branch 'development' of https://github.com/MatterHackers/agg-sharp into development
Created a bunch of function to help transform coordinate spaces both 2d and 3d.
Added to guiwidget some transform to and from parent child spaces
added screen to ray and ray to screen functions in trackball tumble widget
Made it possible to have no selection.
Working on getting 3D interaction objects for editing into the view.