Support for displaying RegisteredService information on login form

Relates to https://github.com/Jasig/cas/issues/539

This pull simply just adds a `logo` field to the `RegisteredService` class, and adds the retrieved registered service instance into the UI context. The UI is then decorated with the logo path and service name and description to display that info when a service request is found. 

Tested with the JSON service registry and worked just fine. 

Sample screenshots:
![](http://i.imgur.com/k52316a.png)

Mobile view:

![](http://i.imgur.com/KsBLQBq.png)
I suppose that technically depends on the JPA-Impl but with Hibernate, it should, yes. Here you are:

```sql
create table RegisteredServiceImpl (expression_type VARCHAR(15) DEFAULT 'ant' not null, id bigint generated by default as identity (start with 1), attribute_release blob(255), description varchar(255) not null, enabled boolean not null, evaluation_order integer not null, logo varchar(255), name varchar(255) not null, proxy_policy blob(255) not null, required_handlers blob(255), serviceId varchar(255) not null, ssoEnabled boolean not null, theme varchar(255), username_attr blob(255), primary key (id))
```