Added ProxyBusObject.MethodCall method

Using the method name MethodCall more closely matches the name found in C++.
The old method MethodCallSynch is still available it has just been marked as
obsolete.

Discovered that passing null in for the MsgArg when the AllJoyn method had no
input parameters cause an error.  Added MsgArg.Zero that can be passed in when
an AllJoyn method has no input parameters.

Modified most unit tests to call MethodCall instead of MethodCallSynch.

Change-Id: Ic0afe575e04c5332ab82ffc6e1f7c587fa4756ff
Unit test for BusAttachment.DBusProxyObj

Added enum for Request name return values.
Fixed BusAttachment documentation error.

Change-Id: Ia850f44c7f131e9fd2fa27e6c34a1ec5795f9689