Order value and internal changes

UI

• Order form now shows the order value in XBT/BTC below amount field

Internal

• Refactoring of how data state is managed and passed down to components (by using new React context API). This should make it easier to add support for futures.
• Added unit tests for scaled order generator

Order execution instructions and chores

• Added support for three new order execution instructions
  • Post-Only. If this order would have executed on placement, it will cancel instead (Guarantees maker fee).
  • Reduce-Only. A 'ReduceOnly' order can only reduce your position, not increase it.
  • Hidden. Order is not displayed in the book.
• App is not restricted to 960 pixels width or whatever it was on desktop and uses full screen width now.
• Upgrade of various packages