Add `checkStatic` command to `runTests.sh`

[oliverklee]

Goal

As a developer, I would like to have a single command to run all static code checks when using runTests.sh even when the Composer scripts is gone.

Acceptance Criteria

• runTests.sh has a command checkStatic that runs all checks that composer check:static runs (also in the same order).
• The command is mentioned in the runTests.sh help.
• The command is doucmented in the manual.