Primary vertexing in AthenaMT

First draft of the primary vertex alg in athenaMT which was made by @lnovotny. The alg is made in a modular way and takes only tracks as input and produces vertex collection with name being passed as argument to the module. There is an option to made all the alg in module (currently just one) signature specific by providing extra string as argument. The module can be easily added to wherever need and has been tested in IDCalo and bjet sequence where it replaced the current bjet prim vertexing. The alg itself has a basic monitoring of few vertex variables (such as x,y,z position) which can be viewed in expert monitoring hist. @jmasik @cvarni @sutt @smh