webadmin: Refactoring in ProviderModel

Removed unnecessary private prefix from variable names to shorten
them, and moved construction of models to the variable declaration to
avoid cluttering in the constructor. This also made redundant their
setters.

Change-Id: Iac82299c44058327eaefc870ec1916d5189bb9e2
Signed-off-by: Lior Vernia <lvernia@redhat.com>