Removed spurious executable bits.
Created a class to contain all the gritty details of PID conversion in one place instead of having every converter repeating near-same code.
Converted urqmd2u to UPIDConverter.
Removed unused PID-conversion code from ampt2u.
evtgen2u: consistently use C++ streams instead of mixing them with cstdio.
Removed unused PID-conversion code from hijing2u.
Converted pluto2u to UPIDConverter.
Converted venus2u to UPIDConverter.
Converted epos2u to UPIDConverter. At the same time, a bit of clean-up in the latter - EPOS, NEXUS and VENUS PID conventions are essentially the same, therefore we only need one conversion table for all three. We call this convention "Werner", after the main author of all three models.
Added therminator2u. Seems okay but needs a little bit more work in order for validation to be completed.