Transformer: size only the graph + toolbar as 400px

Summary:
Sizing the entire transformer widget to 400 created an unfortunate side
effect of wrapping reflection transformation input boxes (since they
tend to be more than 400px wide. This commit wraps only the graph and
toolbar portions in a 400px-wide div instead, letting the transformation
list size itself more appropriately.

Test Plan:
Verify that with the formal mode commit, reflection line input boxes do
not flow onto multiple lines.

Auditors: alex