New flag for PieWidget

• Fixed RadialGroup#isWithinInnerRadius so that it takes into account the totalDegreesDrawn.
• Added RadialGroup#isWithinDrawnAngle.
• Added RadialGroup#isInnerRadiusBlockingPropagation.
• (NOT BACKWARD-COMPATIBLE) Added a new flag: hitThroughInnerRadius (for PieWidget). Default value: true. This changes the way PieWidget#hit behaves: it isn't based on the presence of a background or background color anymore. If you don't want your hit to reach Actors behind your innerRadius, set this value to false.
• (NOT BACKWARD-COMPATIBLE) Renamed PieWidget#isBackgroundHit to PieWidget#isInnerRadiusBlockingPropagation. This is a more appropriate (less misleading) method name based on the new behavior described in the last point.
• Minor optimizations for #findChildIndexAtStage (in both RadialGroup and PieMenu).
• Minor JavaDoc tweaks.

WebDemo updated to use v5.0.0.

For people transitioning from v4, the main difference is with the behavior of the inner radius part: it used to block or not the propagation of the hit method to Actors below it depending on the presence or not of a style.background or style.backgroundColor. Now, this has been adjusted to allow more flexibility: use the hitThroughInnerRadius flag. It only applies to PieWidget and PieMenu, and in both cases really only mostly matters if you were not using any of the "drag" behaviors (that is, you allow the user to release it's mouse-click before letting them select an option).

Basically, if you can't notice any difference when you click in the innerRadius of your toy, then you're good to go! :)