Add filter for local provider name

[soderlind]

Add filter amf/local_provider/name, which allows you to change the local provider name.

fixes #47

[roborourke]

Technically not a bug fix so a patch version change doesn't seem appropriate even though it is backwards compatible. I'm not really concerned about that though.

The intended method to do this is to extend the Local Provider class and swap it / decorate it using the amf/provider filter. I think that's why we left the filter out in the end, to keep things more object oriented - it's documented as using a "Decorating Provider" in the readme at any rate.

I think this filter should at least be documented under this section https://github.com/humanmade/asset-manager-framework#local-media

[roborourke]

Thanks @soderlind. Can I ask what capacity you're using this plugin in? Always keen to understand how folks are using this library.