Merge RarsTest and add a `--validate` option

[privat]

RarsTest was extended to accept arguments (see #47) so you can run it on your own programs to check they behave correctly.
It is then more a tool to test programs (in some CD setup for instance) than a way to test Rars.
However, compiling and running RarsTest is not as simple as running Rars.

A solution could be to integrate the CLI services of RarsTest into the main Rars entry point with a custom option --validate (or something).
This also could be a step towards #39.