Fix pointSize resetting on modify (etc)

Summary:
I was resetting the default properties on every
modify when I shouldn't have been (if we actually want
modify to be like setProps rather than replaceProps,
which I think we do)

Test Plan:
 * Make an interactive-graph
 * set it's type to points
 * smoke test that you can move the point in the editor
   and it updates the correct answer field

Auditors: brianmerlob