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

@@ -17,7 +17,6 @@ import tempfile
 from GRID_LRT.auth.get_picas_credentials import picas_cred as pc
 import GRID_LRT
 from GRID_LRT.auth import grid_credentials
-from subprocess import Popen
 
 from GRID_LRT.safepopen import SafePopen
 
@@ -384,7 +383,7 @@ 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,