Update CCEventTouch.h

MAX_TOUCHES=5 is less than most touch devices, iPad/Android tablets can almost all handle all 10-11 touches. Perhaps a value of 15 would be better? 

Note: There is a #define IOS_MAX_TOUCHES_COUNT 10 in CCEAGLView.mm already for this, but multitouch fails on touch 5 in "void GLViewProtocol::handleTouchesBegin" at the code:- 
            // The touches is more than MAX_TOUCHES ?
            if (unusedIndex == -1) {
                CCLOG("The touches is more than MAX_TOUCHES, unusedIndex = %d", unusedIndex);
                continue;
            }
Merge pull request #7740 from GavinThornton/v3

Update CCEventTouch.h