PtsIO improvements
This MR adds the ability to read and write .pts files in serial and parallel mode.
It also fixes the PtsField constructor not setting the fieldnames, and adds a FieldConvert OuputPts module.
The only thing that is currently missing is proper management of loading pts files in parallel. The current implementation will load a file matching its rank or fail. Neither PtsFields nor files are designed or meant to carry parallization info.
I did not add any tests because currently, we have no proper way of comparing pts files in a platform independent manner. Hovever all test are green on my machine and i just started this branch on buildbot.