Security proxy filter to make basic auth challenge if https and matches user-agent.

This is a fix for:  [Geoserver: ability to "read" protected geoserver layers by ArcGIS client](https://github.com/georchestra/georchestra/issues/60?source=c)

A filter is added to applicationContext-security.xml which checks the user-agent of the request and scheme.  If the scheme is https and the user-agent matches one of the regular expressions the filter is configured with (For example .*ArcGis.* ) and the user has not logged, then a basic auth challenge is made.

If there is a basic auth header then it is validated.

otherwise the filter progresses as normal.