rework key view into fragments to later add certifications

OpenPGP-Keychain/src/main/res/values/strings.xml

@@ -414,6 +414,8 @@
     <!-- Key view -->
     <string name="key_view_action_encrypt">Encrypt to this contact</string>
     <string name="key_view_action_certify">Certify this contact\'s key</string>
+    <string name="key_view_tab_main">Info</string>
+    <string name="key_view_tab_certs">Certifications</string>
 
     <!-- Navigation Drawer -->
     <string name="nav_contacts">Contacts</string>