New feature: OWS request time-out

Adds a new configuration option to the front controller config (main.xml) that allows to interrupt long running OGC service requests after a certain time.

Example:

```xml
...
  <RequestTimeoutMilliseconds serviceId="wms1" request="GetMap">1000</RequestTimeoutMilliseconds>
  <RequestTimeoutMilliseconds serviceId="wms2" request="GetMap">2500</RequestTimeoutMilliseconds>
...
```

Feature proposal:
http://osgeo-org.1560.x6.nabble.com/Feature-request-OWS-request-time-out-td5139289.html