This acomplishes Squish Task[#17737]: Merge group by into the cogwheel
http://squish.ish.com.au/tasks/17737
Columnpicker.js and grid.js have been modified to merge the group by list into cogwheel menu.
Modified grid.js and columnpicker.js
Not to be merged untill next commit.
Using dropdown-menu and dropdown-submenu to create nested list.
Created a nested list for groupby options and column selector.
Made alignment and margin changes with css styling.
Added the tick mark image file.
The cogwheel menu now appears on clicking the icon and disappears
when the mouse is moved out as it originally was designed.
Merge branch 'master' into viks-Merge-Group-by-into-the-cogwheel-Task#17737

Conflicts:
	app/assets/javascripts/grid.js
Merge these changes for adding new filters like
"Today or later", "Yesterday or earlier" etc.
Merge pull request #494 from ari/viks-Merge-Group-by-into-the-cogwheel-Task#17737

Viks merge group by into the cogwheel task#17737
Merge branch 'master' into viks-due-date-filter-task16277
Merge branch 'viks-due-date-filter-task16277' into viks-billing-report-more-than-seven-days-Task#19949