Make project reuse compliant

[damyan]

# SUMMARY

* Bad licenses: 0
* Deprecated licenses: 0
* Licenses without file extension: 0
* Missing licenses: 0
* Unused licenses: 0
* Used licenses: Apache-2.0
* Read errors: 0
* Invalid SPDX License Expressions: 0
* Files with copyright information: 158 / 158
* Files with license information: 158 / 158

Congratulations! Your project is compliant with version 3.3 of the REUSE Specification :-)