cr housing units + evr improvements

Hi guys

Our idea is: We need to improve the shelter management (Configurable).
A shelter must be considered as a "container". Housing units must be defined within all shelters. A housing unit is part of a shelter and we can enroll evacuees in them.
The housing unit management guarantees a detailed management of shelters and evacuees.

We  don't care about the "type" of housing unit: 
If the shelter is a stadium -> housing unit is a tent
if the shelter is a hotel -> housing unit is a room etc
We care just what kind of evacuee could be accommodated.

I added improvements in evr module: added filters, added field descriptions, added report fields 

You /can/ import organisation_id like that, but you should not. That is because organisation_id is a foreign key, and needs to be resolved against an existing organisation record - which is only supported in the <reference> element.

Please refer to other XSLT stylesheets how to import organisation references (e.g. https://github.com/flavour/eden/blob/master/static/formats/s3csv/org/facility.xsl): create an index, import all orgs with tuids, create reference-elements in the target records.