Add keyboard shortcuts `p` and `n` to navigate duscussions.

Mousetrap is used as the help-tool to listen to keystrokes

Added currentDiffIndex getter to store that holds
the index of currently active diff file in the list

Instead of computing it on the component, we will take advantage of it
being available for all components in DiffsApp

Testing keyboard navigation and jumpToFile()

Signed-off-by: NLars Greiss <l.greiss@mediacologne.de>

Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NRémy Coutable <remy@rymai.me>

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/8082

Rename Build to Job

Replace "Builds" by "Jobs" and fix broken specs

Replace "Builds" by "Jobs"

Fix broken spinach test

Fix broken test

Remove `˙` at the beginning of the file

Fix broken spinach test

Fix broken tests

Changes after review

Closes #21218

Updated CHANGELOG

Added docs for filter shortcut

Moved CHANGELOG entry

Added phils fixes

Fixed search form submitting with empty input

Added review fixes

Readability and selector perf fix

Updated shortcuts.png for docs

Updated CHANGELOG

Moved CHANGELOG entry

updated shortcut docs

- Need the `mobile?` detection (that the new version provides) for the
  U2F registration/ authentication flow