Add nucleon initial conditions to the simulation

• I added the new degrees of freedom rho, oldJ and newJ to the simulation. The eom solver as well as appropriate diagnostic modules were updated in regards to this addition.
• I implemented the new diagnostic module ProjectedJInE.
• I added the SuperParticle class containing a whole transversal plane full of color charged point-like particles and functions to interpolate the particle charges to the grid and functions to initialize as well as update the super particles.
• I implemented an option to use fixed boundary conditions.
• I added CgcInitialCondition and CoherentMvModel. Both classes are used to create a nucleon initial condition.
• I changed the build tree for out of source builds. The executables are now found in openpixi_c/build/bin.
• I prevented potential dangling pointers by using smart pointers.
• I added the enums TimeIndex, Direction, Orientation, Velocity, Cutoff.
• I implemented a new sign convention.
• I added the CMake option ONLY_DOC to be able to only build the doxygen documentation.
• I added documentation for all new classes.