i18n linting for .vue files under the
app/javascripts/boards directory

Upgrades prettier to 1.15.3
Runs `yarn prettier-save-all` against the codebase
Most changes are due to https://github.com/prettier/prettier/pull/5519

Reduced the technical debt around our JS flash function by making it a
module that is imported rather than relying on the global function.
The global function still exists mainly for technical debt with how
some requests are being completed, but new JS should import the module
directly.

Also reduces some tech debt in the file by removing the need for jQuery.
Instead Flash is now 100% vanilla JS.

added key to assignee avatar loop

Added some error handling which reverts the frontend data changes &
notifies the user

Fixed users href path being incorrect

Changed how components are added in objects

Does not remove the issue from the selected tab when it it de-selected, it instead gets purged when changing tab