Fixes for inserted padding layer in ResNet-like models

Created by: vloncar

As observed in #305 (closed), padding layer may not compile if data_T and res_T types differ by one having rounding and saturation defined. The same model also demonstrates another issue: If we attempt to insert a new layer after a layer whose output is used more than once the new layer will always be inserted before the first use of that output. This trips up the insertion of ZeroPadding layers and they end up being applied on the same output. Both issues are fixed in this PR.