Extract license check into separate class

[Stefan Glase]

We should offer two methods boolean isLicensed() and String getLicenseError() to be used as shown here:

@Override
protected String doExecute() {
    if (!licenseService.isLicensed()) {
        errorMessage("Unable to start session because of license error: " + licenseService.getLicenseError());
        return ERROR;
    }
    ...
}

Tasks

• implement service
• test service
• use in ScrumPokerAction
• use in ScrumPokerHealthCheck ?
• use in StartSessionWorkflowFunction