fixed bugs:

- work around Mono bug in GZipStream (see http://sourceforge.net/p/keepass/bugs/1373/) by including a custom GZipStream implementation
 - fixed issue with export database to System file picker location
 - fixed issues with preference options crashing with ActivityNotFound (due to changes in Xamarin 5.1, see https://bugzilla.xamarin.com/show_bug.cgi?id=33617
updated manifest/changelog

src/ZlibAndroid/Resources/values/Strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+	<string name="library_name">ZlibAndroid</string>
+</resources>