Code hygiene: Use more generic nicer variable name for headings

Change-Id: I6d706f51e8be2e5a738136163ac73cb27d683c5d
Merge "Code hygiene: Use more generic nicer variable name for headings"
Code cleanup: Separate Overlay, Drawer and CtaDrawer from mf-navigation.js

Change-Id: If1b52a918d3cb457a4d30bd68c2343c0ffc26461
Merge "Code cleanup: Separate Overlay, Drawer and CtaDrawer from mf-navigation.js"
use M.require('Overlay')

If1b52a918d3cb457a4d30bd68c2343c0ffc26461 should have
been rebased before code review. Fixing mistake

Change-Id: I02ba39c30868c8e76ab09391203240f50026f09b
Story 770: Add notifications (user) icon

When Echo is loaded, the icon shows the number of unread notifications
and is a link to Special:Notifications. When user is logged out, shows a
CTA drawer.

Also, removes the search button on special pages in alpha because there
is no room for it anymore.

Change-Id: I7fb40be2ff2fd6988dc2f64110a76a5867300ba2