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 

Ahm - and what it does is whenever the shelter_id field in the form gets changed, it looks up all shelter_units with the selected shelter_id and populates the drop-down for shelter_unit_id with the respective record IDs and names.

The script has recently been reworked and I'm somewhere in the middle of migrating the use-cases to it, so if anything doesn't work as expected, let me know.