Update content for 1.19 release (#2631)

Update version to 1.18 (#2563)

Bump version to 1.16 (#2360)

Update version to 1.15 (#2262)

Bump version for 1.14 (#2203)

Bump version for 1.13 (#2138)

Add Python interop sample notebook (#2066)

This adds a Jupyter notebook sample for invoking Q# callables from
Python. I confirmed the new notebook runs in integration tests as
expected.

Remove configuration in DF chemistry sample (#2045)

This configuration was added in #1700, but it has a wrong error budget
that is not compatible with the other configuration and the sample. I
removed it again for clarity.