Add /incoming credentials to configuration file

Authentication is being added to soledad server so that MX can use the /incoming API (soledad#8854 (closed), soledad#8827 (closed)).

On Leap MX side, we need to:

add credentials to configuration file (default: mx:default_mx_token)
load credentials from configuration file
use credentials to interact with /incoming API
create an issue so platform will write a custom token to MX and Soledad configuration files. platform#8857

Edited Sep 14, 2017 by drebs

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