Upgrade to Gradle 6.7.1 and supporting JDK 11

[g3force]

This PR includes:

• Build the plugin with Gradle 6.7.1 and support JDK 11 (without any warnings)
• Support Gradle versions > 4 in the SEU
• Support the Gradle daemon (close the H2 database after usage, store the database in a repository directory by default)
• Support custom h2 datastore paths that include a ':'
• Cleanup temporary directories in unit tests
• Remove the possibility to add dependencies with 'seuac', as this is not easily possible with JDK 11 anymore
• Load h2 database without the need to add it as a 'seuac' dependency
• Replace Scriptom with a vbs script to avoid the 'seuac' dependency and the native libs