Update strings.xml

It is a general concept, but in title and in following line of the description shows what application it is assigned to.

app/src/main/res/values-el/strings.xml

@@ -165,7 +165,7 @@
 
     <!-- Strings displayed only on Google Playstore. Optional, but good to have -->
     <!-- App title has to have less than 50 characters. If you cannot squeeze it, just remove a part of it -->
-    <string name="app_title">Simple Contacts Pro - Manage your contacts easily</string>
+    <string name="app_title">Simple Contacts Pro - Απλοποιημένη διαχείριση</string>
     <!-- Short description has to have less than 80 chars -->
     <string name="app_short_description">Μια εφαρμογή για τις Επαφές σας χωρίς διαφημίσεις, σεβόμενη το απόρρητό σας.</string>
     <string name="app_long_description">