CMS-3775 Live Edit - Context menu general design fixups

- updated styles for context-menu, item-view-context-menu, tab-menu, appbar-tab-menu
- removed styles from ts code found in AppBarTabMenu.ts
- removed close icon from item view context menu
Merge pull request #811 from enonic/cms-3775

CMS-3775 Live Edit - Context menu general design fixups