Drop-zone interface for importing graphs

[maxhully]

This is isolating onto the upload interface, not taking into account the report interface.

User flow:

• Open "Import graph" page. It invites you to drop a .zip with shapefile data of the VTDs for a state.
• Drop a .zip. A progress bar tells you the upload progress.
• Once uploaded, you see the job status of the graph processing job.
• Once processed, you are directed to the graph report page.