Few improvements for the AdvancedDrawer and AdvancedDrawerController

[JohnF17]

Hello, here are a few improvements I've thought about for this great package.

Improvements

Add the following properties to the AdvancedDrawer

• Allow customisation of the drag start position by adding an optional dragStartPositionOffset parameter
  • Fixes the issue of the drawer just randomly appearing on screen via a horizontal drag on any part of the screen, even the furthest drag opposite from the provided direction. With this parameter the horizontal drag only starts if the drag start offset (got from dragDetails) is less than or equal to the provided dragStartPositionOffset.
  • You can also make it an enum or a percentage out of 100 like 25%, 50%, 75%, 100% (which is the behaviour we have now) and 0% (which'll mean it's disabled)
    • Ex. If 25% is picked, this would mean 25% of the screen from the drag direction would be where the drag has to start to open up the drawer

Add the following methods to the AdvancedDrawerController:

• isDrawerOpen method
  • No parameters
  • returns a boolean
• setGestures method
  • enabled: parameter
  • returns void

Expose many more values to the controller. Thanks