Several changes entered this commit.

* The data structures used by TICL have been moved into
  DataFormats/TICL, that has to be added as a CMSSW package.
  Tracksters and Tile are currently present. The encapsulation of
  std::array as a transient data member of a Tile is due to the fact
  that ROOT natively supports those and refuses to create ad-hoc
  dictionaries. Moreover, at present, an std::array cannot sit at the
  top of a ROOT branch requiring, once again, its encapsulation.
* The "master Tile" has been added as a single producer. A unique Tile
  containing all the 2D reconstructed clusters is created once and put
  into the Event. All iterations will fetch it from the event and mask
  the 2D clusters on the fly. This required also some changes to the
  clusters filters logic. Now the filters produce also a vector<float>
  that represents the result of merging their input mask with their
  own selection. TICL iterations will make use of the filter's
  vector<float> to dynamically mask clusters from the "master Tile".
* The fractions have been added to the Tracksters. The sharing of the
  energy of 2D clusters is flat and based on their multiplicity, i.e,
  a fraction of energy/multiplicity is assigned to all Tracksters that
  use the 2D clusters. Better splitting algorithms can be studies or
  Machine Learning techniques could be put at work here.
* The hits and fraction of the Trackster are now correctly populated.
  This required an additional loop over the components of each 2D
  cluster. In the future the CaloCluster, PFCluster and hits and
  fractions data structures could be reviewed or, at least, TICL could
  use some other, more efficient, internal data representation and
  collapse into the legacy ones only at the very last stage.