Document that org.assertj.core.api.Assertions is now directly usable

Hello AssertJ DB

Following https://github.com/assertj/assertj-db/issues/329 and its PR https://github.com/assertj/assertj-db/pull/330

AssertJ DB Documentation should now mention that it is now possible for both AssertJ DB and AssertJ Core assertions to coexist in the same class with only one static import from AssertJ Core.

I took a look at the documentation to find occurences of the Assertions class full name.

Here are the candidates for modification that I found :

**Quick start**
- Dependency management - https://assertj.github.io/doc/#assertj-db-quickstart-dependency
- Both maven and gradle part should be updated with latest version
- How to use the static import - https://assertj.github.io/doc/#statically-import-org-assertj-db-api-assertions-assertthat
- Title of the paragraph
- Content of the paragraph itself

**Concepts - Navigation**
- With a Table or a Request as root - https://assertj.github.io/doc/#assertj-db-concepts-tableorrequestasroot
- The introductory phrase uses Assertions class full name
- Both samples of code for Table and Request have the static import
- With Changes as root - https://assertj.github.io/doc/#assertj-db-concepts-changesasroot
- Same as above

**Release notes** - https://assertj.github.io/doc/#assertj-db-release-notes
- Add the 3.0.2 - and the 3.0.1 for good measure

As for how, here are my thoughts :

- Using `org.assertj.core.api.Assertions.assertThat` with previous versions of the library would not compile. So developers still using those should not have that as the only reference. So for now I believe the documentation should mention both `Assertions` class.
- However I believe the feature makes `org.assertj.db.api.Assertions.assertThat` irrelevant. And I think the documentation should make it clear that `org.assertj.core.api.Assertions.assertThat` is to be favored.

If documentation is open for contribution, I am willing to do a proposal.