Improve working-set context menu UI/UX

This commit refers to issue #6012
It rearrange items whitin the working sets and move all those related
to "sorting" to a new drop down menu accessible through a new cog
button in the working set header
Reduce cog size to 13px
Reduce cog opacity for non-hover status
Fix cog color and position
Add tests for ContextMenu#isOpen
Refactor work set menu sorting event handler
Refactor RecentProject ext to use ContextMenu#assignContextMenuToSelector
Add @param jsdoc description
Merge pull request #6107 from artoale/fix-context-menu

Improve working-set context menu UI/UX