Support for timeframes in Combo Overlays and Average Overlays

When implementing a combo or average (avg) overlay, it is now possible to use the timeframe values of the input overlay(s). A Water overlay with 10 timeframes should result in an Average overlay with also 10 timeframes.

Combo Overlay example:
ADD(AT,BT); where A and B are input overlays, and T is the number of timeframes. In case A has 10 frames and B only 5, then in B6 to B10 the last value from B5 is used.