Fix sidebar not opening first time
On devices with <992px width (sm, xs), sidebar doesn't open when swh-push-menu is clicked first time.
This was due to webapp-utils.js:5 setting collapseSidebar to false by default on all devices.
Reviewers: Reviewers, vlorentz, anlambert
Reviewed By: Reviewers, vlorentz, anlambert
Subscribers: anlambert, vlorentz
Differential Revision: https://forge.softwareheritage.org/D1583