Feature bash completion

This change adds on-the-fly definition of bash completions for (FOAM_APPBIN) OpenFOAM applications. This makes it easier and less error-prone than recreating the bash_completions via a script and reduces the environment overhead compared to using separate functions for each application. It also makes it relatively easy to provide as a backport for previous OpenFOAM versions.

Tcsh users now get completion as well, but for efficiency the completion_cache should be pre-built (via the bin/tools/foamCreateCompletionCache script).