Clean up setting of options in dynare_sensitivity.m

Currently, it is very intransparent and prone to bugs.

• neighborhood_width forces

if options_gsa.neighborhood_width,
    options_gsa.pprior=0;
    options_gsa.ppost=0;
end

but the manual says that neighborhood_width only works when pprior=0 and ppost=0. This seems like a bug. If we reset options set by the user, we should consistently provide warnings on the screen.

• Even more problematic, without any indication in the manual, using morris=1 overwrites almost all other user-specified options:

if options_gsa.morris==1,
    if ~options_gsa.identification,
        options_gsa.redform=1;
    end
    options_gsa.pprior=1;
    options_gsa.ppost=0;
    %options_gsa.stab=1;
    options_gsa.glue=0;
    options_gsa.rmse=0;
    options_gsa.load_rmse=0;
    options_gsa.alpha2_stab=1;
    options_gsa.ksstat=1;
    options_gsa.pvalue_ks=0;
    options_gsa.pvalue_corr=0;
    OutputDirectoryName = CheckPath('gsa/screen',M_.dname);
else
    OutputDirectoryName = CheckPath('gsa',M_.dname);
end

In particular, that results in none of the user-requested output being displayed. See http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=7115. @rattoma Is there a particular reason for this? I could not find any apparent incompatibility of morris=1 with e.g. posterior sampling.