This PR switches the project to use strict typechecking with Typescript, which unconvers a lot of new errors that aim to help us catch more bugs, particularly around null checks and wrong function calls.

Also improved the types for the Query component a bit, so they are more generic and don't lose type information in functions such as updateQuery or fetchMore. Since these are ultimately functions that live in apollo-client, those should be improved there as well (that will come eventually in a PR to that repo), but I improved the types for this particular case since it's a new component and it would decrease the breaking changes. However, I did improve the types a bit in the graphql HoC, as far as I could (didn't override the types that were imported from apollo-client in this case).

One caveat this new strict mode has (which is a fair one IMO) is that decorators cause errors when used in this setup. They raise type errors in all cases where you define a lifecycle hook (see microsoft/TypeScript#17989). Anyway I think we shouldn't be using decorators with Typescript, both because they are still not a standard, and second because they don't have the exactly same semantics as we intend to use them here (the idea is that we don't change the external API of a class when a decorator is applied, but this is not the case).

Sorry for the big PR, but this implied touching all the files since they all had some sort of error in strict mode.

Also let's discuss if we want to add this as part of the 2.1 beta or if this should be part of a new release 2.2 or something.

Closes #1589