Renames Page's uri() method into path()

As discussed in #527, `path()` is a more describtive name for the `uri()` method. This pull request renames the `uri()` method into `path()` and updates all occurrences in Wolf's core, while still leaving an alias for backward compatibility reasons.

The internal (and private) `uri` property has been renamed as well.

For consistancy reasons, `findByUri()` has been renamed into `findByPath()` as well. As for the `uri()` method, an alias has been created for backward compatiblity.

Some small improvements have been made to the `findByPath()` method to make it more comprehensible. It's functionality has remained the same.