Fix | v1 - Deprecate Invalid Page Property

[Sammyjo20]

This PR introduces a new property to the abstract Paginator class: $this->currentPage. This property should be used as a replacement for the $this->page property especially when used inside of the isLastPage method.

I have deprecated the old page property and getPage method because they would often be one figure higher than they should be. The reason why is with the order of how iterators work in PHP.

1. Rewind is called
2. Valid is called
3. Current + Key is called
4. Next is called
5. Go to step 1 again

The old page property started at 1 on rewind so what happened was:

1. Rewind is called - $this->page = 1
2. Valid is called - No response yet so isLastPage is not called
3. Current + Key is called - Get first page
4. Next is called - $this->page = 2
5. Valid is called - This is the issue - you would expect $this->page to be 1 but it's actually 2

The new currentPage property is now being used internally in the code which starts at zero instead of one and all tests pass.

[Sammyjo20]

Self review