Make luxletter PostgreSQL compatible

[marcellussiegburg]

Currently, a lot of errors are reported when using Typo3 with PostgreSQL. This is mainly due to the usage of "wrong" quotation marks.

These changes enable the usage of luxletter even with PostgreSQL.

[einpraegsam]

Thx for digging into it. In general, I would also like to change doublequotes to singlequotes to be more compatible to the used SQL version.
To access such a pull request, please:

• Don't mix up different stuff in one pull request (e.g. one pull request for single quotes, another pull request for adding commas to ext_emconf.php and another one for adding type hints)
• We don't want strings with double quotes. Please use 'this is a string with a \'quoted\' string'

[marcellussiegburg]

I made two new pull requests #256 and #257. I will add another one (for type hints) once #256 is accepted (because it is affecting the same code lines anyway).

The changes to ext_emconf.php were made by php-cs-fixer so should not be required anyway.