Allow rebranding of Page Title and Logo

[shealavington]

This PR adds some basic flexibility so anyone can take the pulse page and white-label it as part of their own application. This does not break features and adds extensibility.

I didn't write tests for this as there's such a thing as too many tests, and I worry this would be over-testing. If you would like a test for ensuring the slot data is overwritten, I'm happy to take a look?

I've enabled maintainer editability.

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!