Applied BootStrap to AdminHeader and AdminAcountManagement
Aligned Options
Typo fixed
removed sign before button
set table to be responsive
1.put back icon since admin page can be different from other pages
2.moved Instructor Count outside the panel heading
3.renamed the panel heading
4.added admin icon for navbar
Merge pull request #2067 from TEAMMATES/Issue2066

Applied BootStrap to AdminHeader and AdminAcountManagement