feat(Dialog): add width prop

[petegivens]

• Dialog accepts a width prop for custom sizing.
• If width provided is a number, it will be converted to pixels
• Only applies width if Dialog is not marked as fullscreen

[martahj]

LGTM. Verbal verification that it runs locally? 😛

[petegivens]

@martahj omg u want me 2 test it?

jk, yes it works fine locally :)