UP-3912 Admin UI Updates

https://issues.jasig.org/browse/UP-3912

- Added icons to menu items, made them to look like buttons (so they stand out);
- Updated single-entity-select to look like multi-entity-select (without changing functionality, can still only select one);
- In 'Manage Portlets', updated table nav to Bootstrap styles; added icons to table links;
- Permissions manager looks more like Universailty but Bootstrap-y