VE-1605: Introduced new global variable: $wgVisualEditorNeverPrimary

This new global variable disallow VisualEditor from ever appearing as a main/default/primary editor.
At the same time I'm removing old wgForceVisualEditor variable as not needed anymore.

https://wikia-inc.atlassian.net/browse/VE-1605
VE-1594: Initial work on single media tool
VE-1594: Move cart UI and logic to widget. Finalize UI
VE-1594: Removing accidental file
VE-1594: Resign from using StackLayout, cart controls always visible
VE-1594: Tool to open single media dialog. i18n.
VE-1594: Export messages for use in VE
VE-1639: Send AJAX request from ve.ui.WikiaSingleMediaQueryWidget and emit requestMediaDone when results fetched
Merge pull request #5297 from Wikia/VE-1594

VE-1594: Build the appropriate views of image/video dialog
VE-1639: Display search results
VE-1639: Addressing code styling issues
Merge pull request #5296 from Wikia/VE-1605

VE-1605: Introduced new global variable: $wgVisualEditorNeverPrimary
VE-1639: Clear search results when new query is typed
VE-1639: Clear search results when closing dialog
VE-1639: Removed unused variable
VE-1654: Added support for cursoring over results items by reusing OO.ui.SearchWidget.prototype.onQueryKeydown

https://wikia-inc.atlassian.net/browse/VE-1654
Merge pull request #5301 from Wikia/VE-1639

VE-1639: Integrate ve.ui.WikiaMediaResultsWidget into ve.ui.WikiaSingleMediaDialog
Merge branch 've-sprint-31' into VE-1654
VE-1654: Addressed code styling issue
VE-1649: Cart views