Login with basic validation

Added login capabilities
Added very basic form validation ( fields are not empty ), to prevent unnecessary calls to DB.


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For validation see https://github.com/my-koop/module.inventory/blob/beta/lib/validation/index.ts and https://github.com/my-koop/module.inventory/blob/beta/metadata/endpoints.ts. this way you can define a function for validation and use it automatically when you use actions. 
It can also be used automatically in the backend by adding a property `validation` with the function when attaching  a controller. There is no example at this moment though. it would be something like
```
inventoryModuleControllers.attach(
    {
       endPoint: endPoints.inventory.list,
       validation: validationFunctionDefinedInValidation.ts
    },
    itemsData
  );
```
For now you can't access information about the error other than printing it. It should be done as part of https://github.com/my-koop/service.website/issues/215