* Rework the travis file to enable PHPUnit
I realized that unit tests weren't executed on Travis. While working on
this file to enable these tests, I started to think we could simplify
it.
I separated jobs so:
- PHP linter and tests are only performed on PHP 7.3
- Translations are tested separatly so they can fail (it was already the
case but it was hard to understand the way it was done)
- PHP 5.6 only checks syntax issues
- the last job checks css, js, etc. (it didn't change)
PHPUnit is not executed on 5.6 because only the version 5 is available
while the latest version is the 8 (https://phpunit.de/supported-versions.html).
I think it's easier to read (each job is more explicit) but I'm not a
Travis expert so maybe there's some room for improvements.
* Fix failing tests
The category `_name` regression was introduced in commit b323ed084.
I wasn't able to understand when and why Search tests was wrong.
The rest is about upgrade of PHPUnit.