convenience helpers for checking the preset type used to create an entity
convenience helper for checking if an entity is inactive

I figure this is fine to add since InactiveComponent is a so-called
"system" component
add DebugGeometryRenderer class
doc comment
maybe a bit over the top with all these extra overloads?
set depth test enabled
begin() now allows setting whether to enable/disable depth testing
override for begin(), defaulting to disabling depth testing
render using thicker lines
add DebugShader which DebugGeometryRenderer now uses

rendering larger points not implemented yet, need to do a second-pass
render over the points generated in end(), but ImmediateModeRenderer
doesn't allow for this, short of using it to generate the list of
vertices twice
replace RenderContext with ViewContext. use registered "services" to hold the renderer objects that used to live in RenderContext