Configure checkstyle and update code to comply

This commit configures Checkstyle and updates the build to comply with
that configuration. The Eclipse JDT metadata has also been updated
so that the output of Eclipse’s code formatting and clean-up is
compliant with Checkstyle.

The use of the latest version (6.10.1) of Checkstyle has required an
upgrade to Gradle 2.7. Gradle hardcode’s the name of the Checkstyle’s
main class which has changed between version 5 (Gradle’s default) and
version 6.

Closes gh-119

samples/rest-notes-spring-data-rest/.settings/org.eclipse.jdt.core.prefs

@@ -8,6 +8,7 @@ org.eclipse.jdt.core.compiler.debug.localVariable=generate
 org.eclipse.jdt.core.compiler.debug.sourceFile=generate
 org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
 org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
 org.eclipse.jdt.core.compiler.source=1.7
 org.eclipse.jdt.core.formatter.align_type_members_on_columns=false
 org.eclipse.jdt.core.formatter.alignment_for_arguments_in_allocation_expression=16

samples/rest-notes-spring-data-rest/.settings/org.eclipse.jdt.ui.prefs

@@ -13,7 +13,7 @@ cleanup.always_use_this_for_non_static_field_access=true
 cleanup.always_use_this_for_non_static_method_access=false
 cleanup.convert_functional_interfaces=false
 cleanup.convert_to_enhanced_for_loop=false
-cleanup.correct_indentation=false
+cleanup.correct_indentation=true
 cleanup.format_source_code=true
 cleanup.format_source_code_changes_only=false
 cleanup.insert_inferred_type_arguments=false