Update and rename LICENSE to LICENSE.txt

Author: PaulStovell

LICENSE

@@ -0,0 +1,12 @@
+Copyright (c) Octopus Deploy and contributors. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+these files except in compliance with the License. You may obtain a copy of the
+License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed
+under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+CONDITIONS OF ANY KIND, either express or implied. See the License for the
+specific language governing permissions and limitations under the License.