Add LICENSE.txt.

LICENSE.txt

+Here is an information about using components.
+
+Scala.
+Scala is licensed under the BSD 3-Clause License. https://www.scala-lang.org/license/
+
+Scala-xml.
+Scala/scala-xml is licensed under the Apache License 2.0. https://github.com/scala/scala-xml/blob/master/LICENSE
+
+Scalatest.
+ScalaTest is free, open-source software released under the Apache 2.0 license. http://www.scalatest.org/about
+
+Lightbend config.
+Lightbend/config is licensed under the Apache License 2.0. https://github.com/lightbend/config/blob/master/LICENSE-2.0.txt
+
+Sbt.
+Sbt/sbt is licensed under the Apache License 2.0. https://github.com/sbt/sbt/blob/develop/LICENSE
+
+Sbt-assembly.
+Sbt/sbt-assembly is licensed under the MIT License. https://github.com/sbt/sbt-assembly/blob/master/LICENSE
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