Optimize CEpgInfoTag. No more copies, just shared pointers.

@opdenkamp This is the EpgInfoTag optimization we discussed in #5629.  
Furthermore, as far as I remember, "my" preverred way is better wrt efficiency:

=> CEpgInfoTagPtr(EpgInfoTag*) constructor call vs. 
=> CEpgInfoTagPtr() constructor call followed by CEpgInfoTagPtr::operator= call