Further developments about report annotations

[bruntib]

Filtering of report annotations has been done in #3870. The following tasks are to be done:

• The filter option count API functions (reviewStatusCount(), severityCount(), etc.) have the same pattern: an extended table is created which is basically the reports table extended with report_annotations table. This could be refactored so this extended table is generated by a helper function and every other API function uses this one.
• Test cases should be implemented for these counter API functions.