Improved pagination in GCE

This pull request improves the pagination in GCE so it no longer sucks :D The main changes are:

* Removed all `listFirstPage` and similar methods from all APIs.
* All *list* methods have two forms: one to list all records that returns a `PagedIterable` (no params), and one to get a concrete page that accepts a `ListOptions` object.
* The `ListPage` object representing a single page has been refactored and improved and now has a convenience method `toPagedIterable`, that allows converting it to iterate over the pages after a filter operation or similar.
* Refactored all parsers to accommodate the new pagination logic.

In summary, every API only has the minimum and meaningful methods to get a list of records, and the pagination domain objects have been reworked to make it trivial to iterate over the pages.

I've also removed most of the warnings in the project.

/cc @ccustine @danbroudy Could you give a try to the branch and run the live tests? Your feedback on how the new pagination methods look like from a user point of view is appreciated too :)
/cc @adriancole Your feedback is also welcome :)

Will followup more completely later.. maybe :) since maybe I will answer
best now.

One thing to keep in mind that in many cases there will be only one page of
results. In this case the leak risk, as well the bloated class is
unnecessary.

It may be possible in the current design to special case this.

Also we had a meetup with clojure folks back in the day (specifically toni
batchelli) who specifically asked to not have auto advancing mandatory as
it introduces risk of crossing network boundaries on simple iteration. They
preferred to manage their own pagination.

In all, I think this change is a step backwards or at best neutral, from a
user pov. It Is less copy paste from implementer pov.

I am not focused on it or the several other patterns we use, and admit that
we can defer a better list for a new version (maybe v2)

In the mean time, feel free to merge this, taking into consideration what
you feel is most time and version relevant. We can always copy paste these
methods back.