Migrate tests to AssertJ

Mostly thanks to IDEA's plugin: https://plugins.jetbrains.com/plugin/10345-assertions2assertj
There is still a lot of work to do when complex and composite matchers are used.

* Add `awaitility` dependency and deprecate `EventuallyMatcher` in favor
of `awaitility`
* Remove Hamcrest from dependencies and disable JUnit & Hamcrest
static imports to encourage to use only AssertJ
* Migrate JUnit assumptions in rules to AssertJ's assumptions
* Deprecate some custom matchers in favor of existing in Hamcrest
after upgrading the last to version `2.1`
* Replace `ExpectedException` rules with `assertThatThrownBy()`
* Mention `MessagePredicate` in the `testing.adoc`

src/reference/asciidoc/testing.adoc

@@ -227,6 +227,11 @@ assertThat(channel.send(message), is(false));
 ----
 ====
 
+==== AssertJ conditions and predicates
+
+Starting with version 5.2, the `MessagePredicate` is introduced to be used in the AssertJ `matches()` assertion.
+It requires a `Message` object as an expectation.
+And also ot can be configured with headers to exclude from expectation as well as from actual message to assert.
 
 
 [[test-context]]