Add/Remove Toolbar elevation

Reference:

http://blog.iamsuleiman.com/add-a-toolbar-elevation-on-pre-lollipop/
https://www.reddit.com/r/androiddev/comments/2k50fw/elevation_on_toolbar_not_working_on_prelollipop/
https://www.jianshu.com/p/802545cec682

Code snippet:

Add elevation
toolbar.setElevation(elevation);

Remove elevation
toolbar.setElevation(0);