feat(core): Add missing core features

[olivernybroe]

This PR is for adding the missing core features.

• [x] Data providers
• [x] Exception throwing
• [x] Helper methods
• [x] Skipping tests
• [x] setUp/tearDown
• [x] beforeClass/afterClass
• [x] Migrate traits to uses statements

Bugfixes:

• [x] Fix using helper methods in non tests, should not use $this
• [x] Fix adding uses call, if class is extending a custom test case
• [x] Fix overriding methods, not getting converted to helper methods

closes #3

[nunomaduro]

@olivernybroe This is looking so good. Can you update this to use pest 0.2?

[olivernybroe]

@nunomaduro Sure, I'll do it as part of this pr then 👍

Really like how easy it is to have test for this.

[nunomaduro]

👏 👏 👏 👏 👏 👏