Add more Discovery sidebar facets

[alanorth]

As a follow up to #28, we need to add more sidebar facets for:

• [x] Author affiliations
• [x] Authors
• [x] Date issued
• [x] Output types
• [x] CGIAR Research Programs
• [x] Region
• [x] Country
• [ ] Subject – should be 'AGRIS keywords'
• [x] Bioversity subjects (cg.subject.bioversity)
• [x] CCAFS subjects
• [x] CIAT subjects
• [x] CIFOR subjects
• [x] CIP subjects
• [x] CTA subjects
• [x] Dryland Systems subjects
• [x] Humidtropics subjects
• [x] ICARDA subjects
• [x] ILRI subjects (dc.isubject.ilrisubject)
• [x] IWMI subjects
• [x] WLE subjects
• [x] CPWF subjects

Etc etc...

Check which of these are already configured as a searchFilter in dspace/config/spring/api/discovery.xml, then add them as sidebarFacets, ie:

<ref bean="searchFilterCrpsubject" />

[alanorth]

Added CPWF subjects and converted "Subject" to -> "subjects" (lower case and plural, see #41).

[alanorth]

Cross off ICARDA, Drylands, and CIP, as they are currently in testing in 4_x-dev branch.

[alanorth]

Update issue to cross off a few facets we've added.

[alanorth]

Last week we added Country and Region, so I crossed them off the list.

[alanorth]

Added all current center subjects to sidebar facets!

[alanorth]

Everything except "AGRIS keywords" is added, but that's just a change in title, and we'll come back to that later.