Feature/sidenav fix

[KapRom]

• Fixed the horizontal scroll of sidenav
• Fixed the squeezing of main content on mobile version
• On desktop the sidenav is as before - open by default
• On mobile the sidenav is hidden by default, opened is over the main content:

[gmrukwa]

I've just seen this review, after almost 2 months hanging... :D

[gmrukwa]

Fix sidenav