Revert "Don't reassign _POST"

This reverts commit 800f41ace59ec0ab10d625b8fa9b6f9a8a3384b3.
Extract common behavior into method

Fix bug: no services were saved on creation of branchsite.
Clean up
Add comments
Go back to yii helpers
Name labels correctly
Set categories and services without hacks.

Use dropDownList + CHtml::listData instead of the, apparently buggy,
application.components.Relation widget