Change ROOT_URL for Meteor Webapp

@johrstrom how do you feel about creating a new reverse proxy uri method that additionally uses the substitution (supported by apache and/or nxginx) to modify the response from the cryosparc server to reinsert the /<uri>/<host>/<port> at the front of all the absolute paths? The problem we face here (paths in the response do not match) is a common problem among all web servers that use reverse proxy, not specific to cryosparc, so it could be useful to solve the problem generally.