Refactored Theme Management REST API and configuration UI

src/main/java/org/nrg/xapi/rest/theme/ThemeApi.java

src/main/java/org/nrg/xnat/configuration/ThemeConfig.java

src/main/java/org/nrg/xnat/services/ThemeService.java

...ain/java/org/nrg/xnat/services/impl/ThemeServiceImpl.java

...main/java/org/nrg/xnat/turbine/modules/screens/Index.java

...main/java/org/nrg/xnat/turbine/modules/screens/Login.java

...nat/turbine/modules/screens/XDATScreen_admin_options.java

...g/nrg/xnat/turbine/modules/screens/XDATScreen_themes.java

src/main/webapp/WEB-INF/conf/xnat-security.xml

src/main/webapp/scripts/themeManagement.js

src/main/webapp/xnat-templates/navigations/HeaderIncludes.vm

src/main/webapp/xnat-templates/screens/XDATScreen_themes.vm