Gerrit upgrade goodies (3.6 -> 3.8)

[Ilmari Lauhakangas]

Recently TDF's infra team upgraded Gerrit from 3.6 to 3.8, which 
involved quite a bit of wrangling with a new build system. I encourage 
everyone to study the release notes and spot improvements which might 
otherwise fly under the radar:
https://www.gerritcodereview.com/3.7.html
https://www.gerritcodereview.com/3.8.html

If you like to use a dark theme, Gerrit now by default picks it up from 
system preferences and you can control it further via Settings - 
Preferences - Theme.

Some might find the new bulk actions feature useful:
https://www.gerritcodereview.com/3.7.html#bulk-actions-on-search-results-and-dashboard

Not mentioned in the notes, we now see an "(executable)" label in the 
file list of a change for files with that bit set, which helps in 
noticing an unwanted mode change.

Ilmari