This merge commit changes the project's license from Apache License 2.0
to a dual-licensing model, allow the user to choose either
Apache License 2.0 OR Eclipse Public License 2.0.

This change is reflected in the license header of each source file as
well as in the NOTICE and README.md files.

The license change has been signed off by all former and present authors
of the project:
- Sebastian Heppner <sebastian.heppner@plt.rwth-aachen.de>
- Torben Miny (b. Deppe) <t.miny@plt.rwth-aachen.de>
- Leon Möller <leon.moeller@plt.rwth-aachen.de>
- Michael Thies <m.thies@plt.rwth-aachen.de>

Create AASX reading/writing tutorial

Closes #69

See merge request !73

Fixes #69

Using license header template from Eclipse jetty project.

adapter.xml: Finally fix deserialization of empty <qualifier> tags

Closes #132

See merge request !72

Empty qualifier tags are allowed per the XSD schema and a frequently
used in XML documents created by the AASX Package Explorer (i.a. in AASX
package files).

Follow up to 516bf1e7, which tried to fix this, but only replaced the
KeyError with an IndexError.
Fixes #132

model: Fix Referable.id_short property: Update parent Namespace on change

Closes #125

See merge request !71

... enhances tests to catch this bug, as well.

Fixes #125

model: Fix recursive update_from: Don't mess up NamespaceSet references

Closes #127

See merge request !70

test.model.test_base: Add test for function update_from for base.Referable

See merge request !68

Fix some CouchDB and update/commit things

See merge request !64