Upgrade build to boot 2.x

- Pump up version to 2.0.0
- Some generic polish
- All changes around breakage with boot 2.x
- Some boot classes has been moved around
- You can't no longer have binding key ending with
  camelCase.
- New Binder now has illegal keys.
- Some changes to tests as we can directly do end-to-end
  testing with ENV_VAR_FORMAT as normal keys
- Spring data repo changes as now uses Optional
- Remove relaxed binder and its tests in favor of new Binder
- Some mockito api changes
- One Ingored test TextPlainToJsonConversionTest.testTextPlainToJsonConversionOnInput
- Relates to #935

Cache metric export properties

Add code formatting guidelines

Rearranged files

spring-cloud-stream-rxjava/pom.xml

@@ -10,7 +10,7 @@
 	<parent>
 		<groupId>org.springframework.cloud</groupId>
 		<artifactId>spring-cloud-stream-parent</artifactId>
-		<version>1.3.1.BUILD-SNAPSHOT</version>
+		<version>2.0.0.BUILD-SNAPSHOT</version>
 	</parent>
 
 	<dependencies>