Fixed Xcode6.3 warning

[msilotto]

I fixed Xcode 6.3 warning on property delegate of TSTabViewWithDropDownPanel. Property delegate is declared in TSTabView superclass of type id<TSTabViewDelegate>, while in TSTabViewWithDropDownPanel subclass is declared of type id<TSTabViewWithDropDownPanelDelegate>. To keep this working on Xcode 6.3 I added dynamic statement into TSTabViewWithDropDownPanel implementation.