met uncertainty tool (in PAT) fixes for 72X releases

The MET uncertainty tool in PAT has been updated accordingly to the last development changes in 72X releases, and can go to the central release now.

Pat MET names have been also updated in order to match the new naming convention.

Matthieu

this class is just a 2x2 symmetric matrix for which there are plenty of good implementations. Since its not used by anything in this PR, I would suggest we take it out and in the meanwhile get examples of what the developer believes cannot be done by existing implementations.