Changed license from EPL v1 to EPL v2 (openhab#466)

* updated license headers
* added NOTICE files
* moved about.html to NOTICE files
* changed main project license
* updated build.properties
* added files to check to prevent error about missing about.html
* removed license info on p2 feature

Signed-off-by: Kai Kreuzer <kai@openhab.org>

Author: kaikreuzer

LICENSE

@@ -0,0 +1,13 @@
+This content is produced and maintained by the openHAB project.
+
+* Project home: https://www.openhab.org
+
+== Declared Project Licenses
+
+This program and the accompanying materials are made available under the terms
+of the Eclipse Public License 2.0 which is available at
+https://www.eclipse.org/legal/epl-2.0/.
+
+== Source Code
+
+https://github.com/openhab/openhab-core