Migrate state management to redux.
Bugfixes & small enhancements included:
- can click outside the dropdown to dismiss it
- when logged into account that has access to upload to multiple users (not including self - so a Dr.-style account), can no longer submit (click Done) on device selection if you don't have a user selected
- better login error messages
- better surfacing of relevant error details
- cannot switch back to Device Selection (from dropdown menu) when upload in progress; should have "not allowed" cursor and explanatory tooltip
- consistent button styling for OmniPod choose file + disabled when another upload is in progress
- "not allowed" cursor and tooltip when hovering on disabled upload button when another upload is in progress