Resolve "Improve installation reliability"

MR Description

Improves installation reliability

Related issues

• Related to: #18 (closed)
• Closes: #18 (closed)

Acceptance criteria met

• Python path can be manually configured
• pip upgrade shall happen before pip usage
• Automatic tests shall be created to ensure proper behaviour
• treqs installation shall be decoupled from other extension code
• Installation shall check for Python modules first to ensure descriptive errors are always given
• Installation shall work on Windows
  • venv shall be sourced in proper way in Windows
• Extension shows descriptive error if...
  • venv package is missing
  • pip package is missing