svtplay: added variable to hold json keys and updated --get-info function
svtplay: added variable to hold json keys and updated --get-info function

* Added a variable to hold all the important json values, now it should be enough to change them in one position. 
* Info is now parsed into a dict and used with --get-onfo
qnorsten/svtplay-dl,qnorsten/svtplay-dl