Split EF.UST handling from EF.IST and EF.SST

The existing code had the following serious problems:
* when trying to update EF.SST or EF.IST, it would write to EF.UST !
* shell commands were called ust_* even for the EST/IST files

Let's introduce the proper separation between what is shared and what
is file-specific.

Change-Id: Ie55669ca37a4762fac9f71b1db528ca67056e8dd
diff --git a/pySim/cards.py b/pySim/cards.py
index c3766e9..1ed1634 100644
--- a/pySim/cards.py
+++ b/pySim/cards.py
@@ -425,6 +425,15 @@
                 EF_USIM_ADF_map['UST'], content)
         return sw
 
+    def update_est(self, service, bit=1):
+        (res, sw) = self._scc.read_binary(EF_USIM_ADF_map['EST'])
+        if sw == '9000':
+            content = enc_st(res, service, bit)
+            (res, sw) = self._scc.update_binary(
+                EF_USIM_ADF_map['EST'], content)
+        return sw
+
+
 
 class IsimCard(SimCard):
 
@@ -566,6 +575,14 @@
                     sw)
         return uiari_recs
 
+    def update_ist(self, service, bit=1):
+        (res, sw) = self._scc.read_binary(EF_ISIM_ADF_map['IST'])
+        if sw == '9000':
+            content = enc_st(res, service, bit)
+            (res, sw) = self._scc.update_binary(
+                EF_ISIM_ADF_map['IST'], content)
+        return sw
+
 
 class MagicSimBase(abc.ABC, SimCard):
     """