Renaming 'rails-js' -> 'rails-js_route_dispatch

As @andrew2005 stated, the project is currently nearly impossible to find.

I do know the name is somewhat long, but as written in the README it's appropriate.

Also we do stay short in terms of use, as the helper is named `route_dispatch` and the JS side implementation stays with the `Rails` singleton.

Repository name & integrations like TravisCI have to be updated to properly reflect the changes in their paths.
I already updated them in the README to obvious ones.