Transposition of data N-cubes

The transposition engine has been clearly isolated from the GIO (for cube transpositions) and SIC (for variable transpositions) libraries, and has been moved to the GMATH one. It benefits several improvements:

• it supports also 7 dimensions (but could support more, independently of GIO or SIC),
• timings and duration projections have been added for user feedback when transposing larges cubes,
• more transposition codes are supported, including all the 3D permutations.