Provide client-side socket.io namespace configuraton ability

[lkraav]

Follow up from #172 (comment), an issue which is closed, so branching it out here to get a fresh perspective on it.

I would like to run a single centralized browser-sync instance, that handles multiple, project-specific, sync channels. On a central server based workflow, this avoids an engineer working on one project disturbing another engineer working on another project (problematic esp. with ghosting). It seems socket.io namespace feature already has everything we need baked in, which seems like bulk of the workload to the untrained eye. browser-sync client should simply be able to take advantage of this with something like:

<script>
var _bs = _bs || [];
_bs.push('namespace', 'meh.site.com-feature-x');
</script>

Server should detect this during handshake or whatnot and configure its socket: namespace option 1 for this particular connection. An incremental and simpler step forward for proof of concept could also be that server accepts a pre-configured hardcoded array of namespaces it is able to work with, instead of just a simple string value.

Thoughts on feasibility of the above? Is there some huge building block requirement that I'm missing?