Refactor output written to stdout / stderr to log statements where applicable.

The kotlin-logging framework uses SLF4J as underlying logging framework. The
latter framework does not allow to change the desired log level to be changed
at runtime. As ktlint supports the command line flag "--debug" to print
additional logging, it was needed to add logback as underlying logging
framework.

The IndentationRule and the RuleExtension class both changed the logging
behavior based on the environment variable KTLINT_DEBUG. This variable could
be assigned multiple values. This variable is now split into two distinct
variables KTLINT_UNIT_TEST_TRACE and KTLINT_UNIT_TEST_DUMP_AST which can
either be set to "on" to enable TRACE resp. DUMP_AST functionality or
anything else to disable it. End users of ktlint should use the new command
line flag "--trace" resp. the existing "--print-ast".

Solved a bug in DumpASTRule when retrieval of the linenumber results in a
IndexOutOfBoundsException cause by an AST mutation resulting in an invalid
offset.

In RuleExtension improved the logic regarding dumping the AST. When invoked
from the extension, the DumpASTRule print the output to STDOUT instead of
STDERR.

Following needs explicit attention while reviewing:
* Check the way the Gradle dependencies are added. I have little knowledge of Gradle.
* I was not able to find published checksums for the added dependencies, so I have added the Gradle generated keys

# Conflicts:
#	gradle/verification-metadata.xml
#	ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/IndentationRule.kt
#	ktlint/src/main/kotlin/com/pinterest/ktlint/Main.kt
#	ktlint/src/main/kotlin/com/pinterest/ktlint/internal/GitHookInstaller.kt
#	ktlint/src/main/kotlin/com/pinterest/ktlint/internal/PrintASTSubCommand.kt
#	ktlint/src/main/kotlin/com/pinterest/ktlint/internal/RuleSetsLoader.kt

…leset

Note: The jar "ktlint-ruleset-experimental.jar" which previously was used
as invalid jar in the unit test, was replaced in the master branch with a
jar that actually does contain a ruleset provider. Now a new JAR (the
"ktlint-reporter-html.jar") is added which does not contain a ruleset
provider. Also the tests have been changed to check in the normal output
for absence or existence of the warning.

…and what .editorconfig value are applicable from debug to trace

Loglevel debug is enabled by the verbose mode which is commonly used on the CLI to detect
which rule actually is throwing the lint error. This same flag is also used by the build
step which checks the ktlint source code for violations. Due to way too many errors, it
became too hard to find the files/lines which need to be changed.

…ging"

# Conflicts:
#	ktlint-test/src/main/kotlin/com/pinterest/ktlint/test/RuleExtension.kt