Enable per service polling

[plouc]

No description provided.

[juhamust]

On related note, the current interval is 1000000ms, which can cause some issues if Mozaik dashboard is used behind proxy. For example, Nginx drops the connection after 60sec by default (i.e. before the next batch is read)

http://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_timeout

[plouc]

@juhamust, this doesn't solve this issue, but it's a small improvement, #75