Move getters to file excluded from android build (#88)

crypto/message_getters.go

@@ -0,0 +1,13 @@
+// +build !android
+
+package crypto
+
+// GetFilename returns the file name of the message as a string.
+func (msg *PlainMessage) GetFilename() string {
+	return msg.Filename
+}
+
+// GetTime returns the modification time of a file (if provided in the ciphertext).
+func (msg *PlainMessage) GetTime() uint32 {
+	return msg.Time
+}