Client noticed inconsistent reference to embedded ID/ partner ID

[joshuaagee-tray]

In the current Tray.io documentation, Embedded ID is the term used, however in this repo the term used is Partner ID - a client was browsing this repo and testing it and was sent down a bit of a rabbit trail sorting it out. A quick search finds references to partner id in readme.md, and config.js and tray.js in the utils folder. Suggest changing to embedded id for consistency with documentation.

Thanks!