Code quality: added PHPMD, updated workflow

[sreichel]

Description (*)

PHPMD

Added to workflow. The config is there since years, but it never was used b/c of to much "common" errors.

• renamed a lot of variables that does not fit camel-case.
  Note: Underscore-prefix is still allowed but may be removed (?).
• suppressed some errors we cant change in DOCs (usage of Superglobals, silence operator).
• excluded some sniff to re-check later
• baselined some error that could be reviewed in time (empty catch blocks, unused private methods e.g.)

PHPCS: ECG standard

This check was useles. It had only onyl rule (Ecg.Performance.Loop.ModelLSD) enabled and every files was excluded.

Added rules. Some of them could/should be removed/fixed seperatly.

phpstorm

In phpstorms phpcs-config you can only select one config file for code-sniffs, but we have three (default, phpcompa, ecg). Added .phpcs.xml to allow syntax highlighting for all sniffs. Just add this file as custom ruleset.

Note: for custom rules use local phpcs.xml

Minor changes

• dot-prefixed all dev-files (phpunit, rector, ... for cleaner basedir)
• added some script commands to composer.json
• removed a lot of phpcs:ignore comments (not all)

Related Pull Requests

• see Added some dev tools & code sniffers #2400
• see PHPMD: added basic config #2771
• see Add PHPMD to workflow #3482