add hw model info to MyNodeInfo

This allows the android app to get this data without connecting to
the device info service (we are already talking to our mesh bluetooth
serivce)

Also possibly useful for apps that are talking to the radio over serial
(cc @girtsf)

mesh.proto

@@ -284,6 +284,15 @@ message MyNodeInfo {
     /// # of legal channels (set at build time in the device flash image)
     int32 num_channels = 3;
 
+    /// The region code for my radio (US, CN, etc...)
+    string region = 4;
+
+    /// TBEAM, HELTEC, etc...
+    string hw_model = 5;
+
+    /// 0.0.5 etc...
+    string firmware_version = 6;
+
     /// FIXME - add useful debugging state (queue depths etc)
 }