Tag queries should use slug instead of name

[Grégory Elhaimer]

Hello,

Nice work on this bundle.

I've some trouble to figure out why the tag queries use the name attributes instead of the slug.
As the slug guarantees the unicity of a tag, asking for a tag which does correspond to the slug but the name should return the given tag.
This behavior should also be working when getting ressources from a tag.

Considering the tag "This is a tag", and its slug "this-is-a-tag", then

$tagRepo->getResourceIdsForTag('article_tag', 'this-is-a-tag'));

should return all the ressources linked to "This is a tag". In this case, nothing will be returned as the tag corresponds to nothing existing in name colum of tag table.