Add ZF2 MVC specific diagnostic checks

[Thinkscape]

Moved from https://github.com/zendframework/ZendDiagnostics/issues/18

• [ ] Check view_manager template_map and template_path_stack
  • Check for existence
  • Check for readability
  • Lint the PHP code
• [ ] Check Zend\Db connection availability
• [ ] Generic Zend\Cache\Adapter check, optionally probing for capabilities and checking that too.
• [ ] Generic Zend\Session\Adapter check.
• [ ] Try to instantiate all SM services found in configuration and catch exceptions.
• [ ] Is module installed ? (request)
• [ ] mbstring.func_overload === 0 here