Implement the electron vertex for AHDC

[ftouchte]

• Read electron vertex from REC::Particle
• Add parameters for the vertex resolution on r and z (fine tuning to be done later)
• Add a parameter for the CLAS versus AHDC alignement (fine tuning to be done later)
• Make the error on the distance (AHDC::hits:doca) dependent on the ADC and time (first implementation)
• Fix AHDC ATOF matching @mathieuouillon

[mathieuouillon]

Looks good to me.