Here we create a default set for the ext-tx experiment which
includes:

Intra: {DCT, ADST} X {DCT, ADST} + IDTX (identity in both directions)
Inter: DCT_DCT + IDTX

This set is used if indicated in the uncompressed header.

Change-Id: Ic907ada12b4e0c98cabb7c9650ab99942d0c0859