Increase Flow coverage

[shaynak]

This is really a bunch of tasks of adding flow typing to individual files but:

• Add flow typing to all stores
• Add flow typing to all action files
• Add flow typing to all util + constant files
• Add flow typing to all chair views + associated components
• Add flow typing to all delegate views + associated components
• Add flow typing to all advisor views + associated components
• Add flow typing to registration views

Ensure that any types are avoided as much as possible -- after this initial addition of coverage is done, we should ideally move to using flow-strict.