Move SafePopen to its own submodule

Having SafePopen in GRID_LRT.application.submit apparently gives some problems if other (sub)modules that use it are imported before the class is defined in submit.py. This moves it to its own submodule GRID_LRT.safepopen to avoid that.

GRID_LRT/application/submit.py

@@ -384,7 +384,7 @@ echo Created job directory $JOBDIR
 cd $JOBDIR
 {launcher:s} {db:s} {usr:s} {pw:s} {tt:s}
 """
-	slurmfile = slurmfile.format(ncpu=int(self.ncpu),
+        slurmfile = slurmfile.format(ncpu=int(self.ncpu),
         queue=str(self.queue),
         njobs=self.numjobs,
         concurrent=self.parameter_step,