Changes to Buildbot web interface

Wish list of changes to the Buildbot web interface.

This can be split into different tasks if some tasks require a lot
of time to get done or require more discussions.

• Main page:
• https://buildbot.mariadb.org is probably only useful for
  someone maintaining buildbot.
  Better to move this to a new page "Builders" and as landing page use
  something more close to:
  http://buildbot.askmonty.org/buildbot/
  We definitely want to have direct links to builds for 10.2, 10.3... and
  all major pages for buildbot.

• Grid view:
• Remove tags from each row and add tags that can be checked/unchecked on top
  of the page. We want to be able to see as many builds as possible
  on each row
• Add revid and tree to the header of build column. These are very important
  to get an idea what is building and to find your commit. See
  http://buildbot.askmonty.org/buildbot/grid
• When clicking on a build header, you get first a screen with 'author' and
  other things for 1/2 second and then you get moved to the git commit.
  This is annoying, remove the in between screen!
• Grid view doesn't show all builds
  For example:
  https://buildbot.mariadb.org/#/grid?branch=10.5
• Shows a lot of builders
  https://buildbot.mariadb.org/#/grid
• Shows only a few. Should show all
• (Rasmus suggestion): Preserve the branch dropdown so that branches can be easily switched.

• Build view
• When clicking on a test, you have all mysqld.err.1 files there which takes
  up a lot of space. Can you get this folded/hidden so that you have to
  click on a 'error files' to see all of them? Same thing you do now
  with 'compile'
• Old buildbot did show the failing test (Search after "Failing
  test(s) in the output") in the header if something fails. Please add
  this information to the (8) 'test' header! Would be good to also
  add for this to each failed build on the grid screen (at least 80
  characters of information!)