series: Display historical cover letters

Cover letters are now using details/summary HTML block to be expandable
with the latest one being expanded by default.

Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
1 job for master in 1 minute and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #321922
test

00:01:21

 
Name Stage Failure
failed
test Test
pep8 run-test-pre: PYTHONHASHSEED='363815268'
pep8 run-test: commands[0] | flake8 patchwork patchwork/bin/pwclient git-pw/git-pw
patchwork/views/series.py:52:80: E501 line too long (90 > 79 characters)
ERROR: InvocationError for command /builds/patchwork-fdo/patchwork-fdo/.tox/pep8/bin/flake8 patchwork patchwork/bin/pwclient git-pw/git-pw (exited with code 1)
___________________________________ summary ____________________________________
py27-django111: commands succeeded
py36-django111: commands succeeded
ERROR: pep8: commands failed
ERROR: Job failed: exit code 1