Usage improvements

[igorkulman]

This PR adds a few improvements I came up using the side menu in my project

• delegate method to know when the menu is animating: useful to update status bar appearance when the menu is dark and the VC light or vice versa
• property to hide / disable the menu completely: useful when you want to have the menu enabled in your root VC but not in any pushed VCs
• exposing a property to know if the side menu is opened or not when not using the custom navigation controller

[evnaz]

@igorkulman Thanks for the contribution. I find these changes useful. Though I have concerns regarding calling a delegate method inside an animation block. Please see my comment for a possible solution.

[evnaz]

I anticipate some unexpected side effects on the use site if the delegate method would be called inside an animation block. Instead I would suggest introducing another two delegate callbacks with an isAnimated argument and call them before scheduling the animation:
sideMenuWillOpen:isAnimated
sideMenuWillClose:isAnimated
I see this as a more universal approach.

[igorkulman]

This is a good point, but my specific case requries the delegate call inside the animate method so the statubar changes gradually not at once wzen animation startes or finishes.