Bug Fixes, Style Changes and Enhancements wrt Server Manager
- Added tristate option for three states (true, false or null) for contrailCheckedMultiselect and corresponding style changes and installation commands
- Fixed optgrouptoggle function re-initializing issue wrt checkedMultiselect
- Added Empty option handling for contrailCheckedMultiselect
- Extended setCheckedState for checkedMultiselect with setting multiple states for the input checkboxes

Change-Id: If0a421f1eaf0cb97b47833c30bbcba98ec9b0cef