Localisation updates from https://translatewiki.net.
Changed version to '1.3.0-beta.2-dev' [skip ci]
Install: Use foreach to check for obsolete config files
Install: escape strings inserted in config_inc.php

This ensures it is not possible to inject arbitrary PHP code into the
generated config file.

Fixes #12908, #17012
Simplify config file generation

- Use a ternary operator
- Remove redundant instructions to manually create the config file in
  label: what the admin needs to do should be clear enough with the
  error message and the text below.
- Improve message to add lines to config file
Remove table background color

This makes the display of the various sections consistent (prior to
this, some had borders around cells and others didn't).

Also, bgcolor attribute is not supported in HTML5 so it makes sense to
remove it for future compatibility.
Remove ellipsis
Start with 0 if given invalid install step
Display section title when starting with step 2