Get rid of Reflect.hasField() check - wasn't working for properties
Remove the "tpl" option from Widget.

They can just override get_template() instead.  It makes it far easier
to instantiate widgets using reflection if we don't have to worry about
constructor arguments
No longer require argument tpl when instantiating widgets
Removed documentation, keeping all of that out of the repo for now

Will put in the wiki when it's ready