Convenience methods for implementing main().

Added a method to TrajectoryAnalysisCommandLineRunner that allows a
one-line main() method in user tools, removing some boilerplate code
that could break with Gromacs changes.  Forward the actual
implementation to CommandLineModuleManager, allowing it to do the same
processing as it does for the wrapper binary/symlinks to it.  This
allows for some simplification of TrajectoryAnalysisCommandLineRunner.

An extra method that runs any
  int (*method)(int argc, char *argv[])
method that calls parse_common_args() as main() through
CommandLineModuleManager could also be added, but left out of this
change for now.

Change-Id: I0b0d626fda50abe04c16e90a1c876262dcff81a4