Added support for the new append method from NZBGet 13+

NZBGet 13 will probably be released in the next few days. This version has a new combined append method that supports both nzb urls and content. Also the return value was changed form boolean to integer (NZBID or error number).

The old methods append and appendurl are now Deprecated, so it's more future proof to add the new method now.
Mipsel PVR with 256 MB RAM (don't forget OS, nzbget, ... has to run on it too) And there are other devices like raspberry pi that also have not much resources. 

I did do it this way because each extra line costs performance on such devices... since python is a interpreter language. 

Of course it can be written the old python 2.4 complex way. I would think since this syntax is standard since the already very old python 2.5 it's not necessary and anyone using/coding python for more just playing around should know this syntax. And in the end you can add a comment line to explain the inline if else for people that don't understand it.

In the end if we don't use the new syntax we can simply don't do it at all, since the old methods (append, appendurl) are still supported by NZBGet for compatibly reasons and simply using the new append method in the old python syntax is a bit pointless to me.