Added Meson reconstruction and possible GTreeManager structure for output
USER: Full changes to Particle reconstruction and GTreeManager (responsible for the output of analysis trees). This commit contains the first code to output trees post reconstruction. Full meson reconstruction is performed including a reaction 4-vector check which includes charged pions to properly reconstruct mesons below 1.6 GeV. A chi-style fit which includes a width parameter is included which improves meson reconstruction (and reduces any bias towards the reconstruction of one particular meson). A pseudo sort function has been included into GoAT to also include the possibility of creating small tree files for fast physics analysis in particular analysis.