Enhancement - parameter to denote the base_url the webserver should run on.

[extorn]

As per this discussion Motion-Project/motion#1508, it would be really useful to permit definition of a base_url parameter for the project. This is needed when using it on a server behind a reverse proxy (such as nginx).

e.g. I expose it through https://myserver/birdbox

The issue is that the references to hostname mean it accesses for example the config.json at https://myserver/config.json NOT https://myserver/birdbox/config.json.

This could be achieved by adding a parameter to your motionplus.conf file and add this to the end of the full host name given if not localhost which would avoid my need for rewrites in nginx to 'work around' the issue (luckily no conflicts with existing resources at https://myserver that I cannot move.

[extorn]

I've coded "a solution" for this. It's in pull request 16 (#16)