Validate all mappings

[visola]

User Story

As a user I want to know if my mappings is wrong as soon as possible.

Acceptance Criteria

• Load mappings during startup
• Add a framework to create validators for mappings
• Execute the validation when loading the mapping
• Make sure it works with Link to server in Admin is broken when starting with no SSL #7
• Expose validation errors in the Admin UI

[visola]

This will need to be reworked after merging branch one to master.