🚀 supercharge tags performance

[kevinansfield]

closes TryGhost/Ghost#8540

• use {{vertical-collection}} in the tags dropdown filter list, opening the dropdown is now virtually instant as it's not attempting to immediately render components for every tag in the list
• remove pagination/infinite scroll from tags screen
• load all tags when accessing the tags screen
  • will pause to show spinner if no tags have previously been loaded
  • if tags exist in the ember data store, show the list immediately and load/update list in the background
• use {{vertical-collection}} to render enough tags to fill the scrollable area with a small buffer and use occlusion and element re-use to swap tags in whilst scrolling (suuuuper fast no matter number of tags loaded)
• scroll tags into view when they are selected (keyboard nav now makes a lot more sense)
• tested with 875 tags and 2x/5x CPU throttling with no major slowdowns 🎉

TODO:

• implement {{vertical-collection}} for the tags dropdown to speed up rendering
• see if there's a way to scroll to tags that are in the occluded area
  • edge-case, only relevant when accessing the individual tag route directly - everything works at the moment but the active tag isn't scrolled into view
  • may be possible by using tag index and scrolling to calculated height rather than using browser's element.scrollIntoView())

NB: I'm leaving the scroll-to-tag TODO for now, it's a nice-to-have for an edge case and we can re-visit if needed later once the tags screen has been redesigned

[coveralls]

Coverage decreased (-0.2%) to 72.893% when pulling e116697 on kevinansfield:soo-many-tags into a057412 on TryGhost:master.

[coveralls]

Coverage increased (+0.1%) to 73.224% when pulling e7b378e on kevinansfield:soo-many-tags into a057412 on TryGhost:master.

[kirrg001]

👍

[kirrg001]

When i run grunt dev i see now:

===================================================================
	Vertical Collection
	:: Including CSS for Visual Debugger
	:: (included in non production builds only)
	:: To use, set {{#vertical-collection debug=true}}
	:: To debug your applied CSS rules, set {{#vertical-collection debugCSS=true}}
===================================================================