Fixed issue #6

Breaking changes :

• now all canvases by default will not generate CANVAS_DRAGGABLE_PANEL, to enable it, you will need to manually check it on the VRTK4_UICanvas,
• optimization to only look for canvases that are directly intersecting with the pointer's ray.

Fix :

• world object on all Layers block UI casting, if the VRTK4_UICanvas is set to be blocked by 3D/2D objects

Updated dependencies :

• Zinnia 2.0.0
• Pointer Interactors 2.0.5
• Interactables 2.0.1
• Combinedactions 2.0.1

• updated Readme.md
• updated Installation/Readme.md
• updated prefabs and scene ( no more missing prefabs)
• updated usage - simplified to use on a single Interactor Prefab.

• it is now faster -> removed custom check for graphic raycast
• depth is now a function of depth + sorting layer*100 + sorting order ( added additional tests)

• fix for -1 pointer id ( not found)

• when used with other EventSystems -> VRTK4_UI_Canvas will check for VRTK4_EventSystem (required for Unity Automated QA)

• fixed issue when camera is disabled, but still using events
• fixed editor errors

• adding feature Block Click Once for custom dragging ( click event will not be used if pointer-> ExplicitBlockClickOnce is set to true)

• fix for disabled pointer (paused/unpaused/custom disabling of pointers) - no event will be used for null/ disabled pointers