Add mockup.html
Split app into tide levels/window, enable buttons

Now you can switch between tide levels and tide windows by clicking on
the links in the navbar.
Add static version of tide levels site to React
Move state TideWindowsInputBox to PilotPlannerApp
Tide-levels now populated from state, calls API

A couple of problems outstanding:

- there are too many tide levels displayed (120) - we need to be able to
  specify time intervals
- the date and time inputs can't be changed at the moment
WIP allow date and time to be changed