Issue #2271529 by attiks, alexpott, Lowell, YesCT, Jelle_S | mdrummond: Move breakpoint settings to theme and module *.breakpoints.yml files at root level.

Issue #1913510 by erich_s, jibran, scresante, nod_, mitron: Core Javascript Files Not Using Standard Indentation.

Issue #2139571 by jessebeach: Underscore.js fails to compare DOM nodes correctly; Toolbar JS will fail when upgraded to Backbone 1.0.0.

Issue #2058843 by rteijeiro, jessebeach: Be consistent with respect to which strings within JS code should be overriddable via drupalSettings.

Issue #1927174 by jessebeach, Wim Leers, nod_, Gábor Hojtsy: Complete the work to make the Toolbar administration menu sub tree rendering more efficient.

Issue #1860434 by jessebeach, Mark Carver, Wim Leers, droplet: Refactor the Toolbar JavaScript to use Backbone; fix several poorly functioning behaviors.

Issue #1938044 by hass, jessebeach, Dragan Eror: Fixed Prefix all toolbar classes to prevent theme clashes.

Issue #1847314 by oresh, jessebeach, mattimck, nod_: Fixed Reduce the dependency on JavaScript for the toolbar to display properly.

Issue #1363112 by mparker17, mgifford, tlattimore, Jacine, dcmouyard, bowersox, ry5n, ahdiaz: Simplify names of 'element-x' helper classes.

Issue #1847084 by jessebeach, trawekp, LewisNyman, nod_, tarekdj: Fixed Vertical toolbar doesn't work with overlay (measure/track displacing elements better + provide change events for them).

Issue #1847198 by benjifisher, jessebeach, effulgentsia: Update the structure returned by hook_toolbar().

Issue #1858576 by David_Rothstein, jessebeach: Fixed The  variable in toolbar.js is set to an empty jQuery object after an AJAX request.

Issue #1137920 by jessebeach, lewisnyman, tkoleary, Bojhan, webchick, benjifisher, nod_, sjbassett, kathryn531, effulgentsia, Everett Zufelt: fixed toolbar on small screen sizes and redesign toolbar for desktop.