Add ZF2 MVC specific diagnostic checks

[Thinkscape]

Moved from zendframework/zend-diagnostics#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