Add license checking (#1353)

It's stated in the Guidelines that all contributions must be under
the Apache License 2.0. To avoid potential mistakes from manual
reviews, this patch adds the check-license.py script to
automatically check all source files for license headers.

Travis CI is also configured to run the check.

Fallout: it turned out that some files already in the code base
either miss a license header or have some minor typo differences.
The patch fixes up some of these deficiences.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

targets/zephyr/src/main-zephyr.c

@@ -4,7 +4,7 @@
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
- *   http://www.apache.org/licenses/LICENSE-2.0
+ *     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