Flag volunteer verified by organisation

[landovsky]

As an organisation, I want to flag verified volunteer to indicate she/he passed my quality standards.
Context: It's up to organisations to verify volunteers and it's up to them how they do it. When org's coordinator is later assigning requests to volunteers, he will be drawing from pool of verified volunteers.

Definition of done

• coordinator can create the verification from volunteers detail
• the verification of volunteer is scoped to the organisation
• the volunteer detail has a row "Dobrovolník ověřen" showing name and datetime of coordinator who verified the volunteer or "neověřen" if no verification is recorded for this organisation-volunteer pair
• upon persistence, the system will store information on when / who verified the volunteer
• usage of modal window for creating the association is nice to have

Out of scope (will be solved in separate story)

• coordinator can remove the verification

[landovsky]

@snopedom @Vratislav please clean-up the story from tech perspective and mark as ready for dev.