* created a method remove_all_except() in scene.py and interactive_scene.py
* Made it such that default mobject colors can be set through the yaml config file.
* * Default color initialisation wasn't working.
Changed conditional expression to `or` instead.
* Added default values to yaml file.
* added set_background_color() function to Scene class
* Changed default font back to Consolas
* Only use -no-pdf for xelatex rendering
* Instead of tracking du and dv points on surface, track points off the surface in the normal direction
This means that surface shading will not necessarily work well for arbitrary transformations of the surface. But the existing solution was flimsy anyway, and caused annoying issues with singularity points.
* Have density of anchor points on arcs depend on arc length
* Allow for specifying true normals and orientation of Sphere
* Change miter threshold on stroke shader
* Add get_start_and_end to DashedLine
* Add min_total_width option to DecimalNumber
* Have BackgroundRectangle.set_style absorb (and ignore) added configuration
Note, this feels suboptimal
* Add LineBrace
* Update font_size adjustment in Tex
* Add scale_factor parameter to BulletedList.fade_all_but
* Minor import tweaks
* Add play_sound
