Massive refactor to simplify codebase

[markormesher]

Notepad for issues I plan to address in a big refactor in the near future.

• [x] Simplify Webpack / general build chain
• [x] Use types instead of interfaces for props/state
• [x] Simplify profile selection into API call + reload
• [x] Remove most (all?) of the Redux plumbing - keep state local to a component where possible
  • [x] Accounts
  • [x] Auth
  • [x] Budgets
  • [x] Categories
  • [x] Dashboard
  • [x] Envelopes
  • [x] Exchange rates
  • [x] Global (what even was this?)
  • [x] Nav (this one might need to stay?)
  • [x] Profiles
  • [x] Stock prices
  • [x] Transactions
• [x] Shared utilities for getting account list, category list, etc.
  • [x] Cache these values
• [x] Shared utilities for fatal and non-fatal errors (kill the app / show a toast?)
• [x] Remove pointless tests (all FE tests?)
• [x] Move modal logic into a superclass?
• [x] Migrate to functional components where possible

[markormesher]

Will close #45