Issue #72 - Fix build failures when trying to use venv and install python packages

[richard-axual]

This PR provides a new Dockerfile to build the KSML Runner and KSML Data Generator images.

It fixes the problems by

• Using a dedicated KSML user (id 1024) which owns the GraalVM/Python installation.
• Adding a fill GCC/G++ build stack to allow Python packages to be build
• Adding other required utilities such as tar, curl and gzip
• Download scripts have been optimized to download and extract in one step

The multistage build allows for very efficient target images .

Tested by

• installing numpy as specified in the issue
• Running the KSML container against a real Kafka and topic
• Running the KSML Data Generator against a real Kafka and topic

Closes #72