based on feedback from @rschamp, thanks!
1. make `ref` into method
2. remove accidental inclusion of prototype modal
3. use `omit` for props so that we don’t need a separate object for wrapped component properties
1. Split out base modal stylings from iframe modal stylings
2. Move iframe-specific stylings into a separate copmonent
3. Move width/height iframe stylings to scss
4. Change global stylings for modals to match #980
5. Update styles to use trello style guide
