tidied up pathmatics

- the god object now lives in the main .m file
validate() now works for mixins

- grob classes’ validation functions look at the entire inherited set
of kwargs (thanks to the Bequest metaclass)
- the mixins themselves only look at their locally defined kwargs
(currently useful for StyleMixin in particular)
safety first

- better style arg validation
- disable screen fonts (which can mess w/ metrics)
- text-storage changes are wrapped in editing flags (though i’m foggy
on how necessary this is given the use case)
cleaned up Text init

- FrameSetter now takes a size arg for the main textframe
- removed some unnecessary arg-juggling in the Text initializer
- removed `del` support from the FrameSetter’s list methods