SUMCONE functor and WeightedRelTableAlg

To complete the transition from LoKi to ThOr syntax for the SUMCONE functor, cover the general point discussed on the issue #272 (closed).

Currently implemented:

• ARG functor, for retrieving the first or second element to which it is applied on the base of the index value
• DETA, DPHI and DR2 functors, which evaluate the respective quantities from each particle-particle combination.
• COMB_MASS functor, that combined mass of the candidate and the reference particle (see !2755 (closed))
• The functionalities required by !2815 (closed)
• RPPVIPCHI2 functor, checks the minimum impact parameter chi2 for candidate particle wrt the primary vertex of the reference particle
• SHARE_BPV functor, checks if candidate and reference particle are sharing the same primary vertex
• WeightedRelTableAlg, an algorithm that receives as input the range of reference particles and the range of candidates. It is configured through a functor that determines the relations between particles that have to be selected (through a boolean WEIGHT value). The algorithm returns a RelationWeighted2D table.
• SUMRANGE functor, which sums a given input functor over a range of particles (from the TO side of the table).
• SUMCONE is an instance to MAP_INPUT_TO_ARRAY with RelationTable = LHCb::RelationWeighted2D<LHCb::Particle,LHCb::Particle, double>

Commented out atm the functor VTX_FIT_CHI2 (check the "good-quality" of the vertex-fit and to cut on its chi2), which throws an exception while trying to bind to the algorithm which is not Condition holder. Need to be investigated further: planning to come back on it later.

TESTS:

• Rec
• Moore (Moore!1461 (closed))
• DaVinci (DaVinci!665 (merged)) -> Implement it once merged

TODO:

• Create a ThOr functor to replace DeltaR2() function, which accepts a range of particles and evaluates the dr2 for each possible combination;
• Configure the algorithm through external functors;
• Generalize the algorithm also for !2755 (closed), !2815 (closed) and other purposes...
• Test for track-like and composite particles

FYI: @mvesteri, @poluekt, @fpolci, @rmurta, @graven, @johndan, @roneil, @jugarcia