Summary: This change gives priority to a user option settingsString to set up the flipper-server configuration and load them from a json string. Also giving the user the chance to avoid flipper-server looking at the launcher config files in the computer
Reviewed By: mweststrate
Differential Revision: D34210110
fbshipit-source-id: 9e852b79da106b5140c59116fd7d0c0f3155e620