[WIP]Have Required validator trim strings to fix #2361

[chesedo]

This will cause the Required validator not to consider fields that has
only spaces or new lines to be regarded as valid. This is done by
checking if the trimmed version of the string is valid.

[chesedo]

Check my next PR where I highlighted that this is also possible in MaxSize, MinSize and Length. That solution will fix it for all validators where this is possible, but it only works for structs called by reference on the validator.Valid() method.

This one will work for all validators called directly (eg. validator.Required()), but will still leave the field 'dirty' and it would probably go into the DB with the padding spaces.

So I would like advise on which solution you would prefer (or both maybe)? If this one will be used, then I would like to also add it for the validators mentioned above before it is merged.