Signup Modal doesn't display if rerunning an analysis

[aarondr77]

It is possible to skip the signup screen if there is already an analysis_to_replay.

1. Create an analysis in Mito
2. Clear your email from the user.json
3. Rerun the mitosheet.sheet() call and notice that the signup modal flashes on the screen but goes away when the analysis is done replaying.
4. Continue using Mito and the signup modal does not appear.

Note: The next time you create a mitosheet.sheet() call, however, the signup modal will appear.

[aarondr77]

Proposal: check the props.userProfile.userEmail on each render and if it ever becomes undefined again, then display the signup modal. Kinda overkill perhaps.