IdStory Identity Manager

I implemented a new filter option for virtual system requests. It searches for requests according to the implementer identity. More than one identity can be selected. Implementers set to virtual system both by identity and by role are looked for.

Please could you do a feedback for me. Especially the JPA predicate form. Thank you.

https://github.com/bcvsolutions/CzechIdMng/commit/683e1c809ddc0349ba56d42c2be0a2d72a22b01b

I did test and codeview, it works and code looks nice, thx!

Review notes:
- Selected implementers are used in "IN" clausule => it can fail, when more than database supported count of parameters will be given (e.g. 2100 for MSSQL in default setting, 1000 for Oracle). I hope no one will use it this way, but exception can be added the same way as here https://github.com/bcvsolutions/CzechIdMng/blob/develop/Realization/backend/core/core-impl/src/main/java/eu/bcvsolutions/idm/core/model/service/impl/DefaultIdmEntityEventService.java#L83 to be more robust. I will add this exception to other places (filters) too.

I did some quick cosmetic changes only:
- CollectionUtils can be used to cover "implementers != null && !implementers.isEmpty()"
- removed redundant "build.add" criteria with just one criteria

Commit:
https://github.com/bcvsolutions/CzechIdMng/commit/4c082fb118cd2a3b61caf2ff3936967a63ae9313

I moved implementation of better exception, when more than database supported count of parameters is given in filter parameter to related #2519.