[DS-1819] Discovery filters encoding

The filters aren't always properly encoded on the discovery pages, take the following url for example: 
http://demo.dspace.org/xmlui/discover?filtertype_0=title&filter_relational_operator_0=contains&filter_0=test++%26+test&filtertype_4=title&filter_relational_operator_4=contains&filter_4=&submit_apply_filter=Apply&query=test&rpp=5&sort_by=dc.title_sort&order=asc 

When navigating to the next page the "test & test" filter loses the ampersand.