Update eng ticket board to be more readable

[nickvisut]

• [x] put "engineering" label on all tickets with "[ENG]"
• [x] add "engineering" label to tickets that appear to be missing it
• [x] note in README or CONTRIBUTING that "engineering" label is required for eng tickets
• [ ] ~create GitHub issue template that a) automatically adds "engineering" label b) automatically assigns issue to project Compass~
• [x] look into adding priority labels
• [x] finish setting up Eng tickets board view to match filter of Eng tickets list view
• [x] create GitHub issue template for more structured issues

[nickvisut]

added "high priority" label for now; can rename later if need be

[nickvisut]

moving following:

• [ ] create GitHub issue template that a) automatically adds "engineering" label b) automatically assigns issue to project Compass

to another issue #415