PET:  Latest version of the IDIF.  User does NOT have to specify the dominant direction anymore.  Also the meaning of the seed is changed - User just have to place the center of the seed on the vessel.  Other parameters, such as max vessel length, are enabled.

Added L1/L2 optional residual metric to  Sokoloff'79 (short) model.

Completely re-enginered the Sokoloff-79 model (as in Wai's implementation = short formula).

a) Enabling the analytic integration, instead of PWL-functions.  This also eliminates the need for the 1-sec upsampling of the TAC data used in the old version.

b) More streamlined and corrected implementation of the Ta-arterial delay.

Re-enabled ABT subtest for the "Liver DCDI-standard model"