Reimplement toolbox, change breakpoints, etc.

• Center firstHeading on small
• Combine the page tools and user tools dropdowns. Some languages' terms for "page tools" and "user tools" are much longer than they are in English, so keeping them separate takes up a lot of space and makes it harder to pick a good breakpoint between medium and big. The two dropdowns have been combined into one to free up space.
• Trigger sidebar with hamburger button on medium. Keeping the sidebar open on medium wastes a lot of screen real estate.
• Adjust the small/medium breakpoint
• Increase font size for small in dropdowns and sidebar
• Minor tweaks like fixing padding of items in toolbar
• Add Wiki tools and Languages to sidebar
• Turn watch button into an icon, place by view/edit/history buttons
• Reimplement the fixed toolbox. This time it uses a combo of position: sticky and pure JS (no jQuery) for applying a .refreshed-toolbox-fixed class. This should reduce scroll jitter.
• Reorganize the JS

Change-Id: I1e0868be00d96f00552281a64d7ae57777889c53