Add support for Traceability Matrix Tables

[Witiko]

This PR makes the following changes:

• Collect and store Learning Objectives in data structures, see the demonstration in #61 (comment).
• Add markup for Business Outcomes to example document.
• Collect and store Business Outcomes in data structures.
• Add markup for Business Outcomes to other repositories that currently contain business outcomes:
  • https://github.com/istqborg/istqb-ct-qdo/pull/30
  • https://github.com/istqborg/istqb-ctal-ta/pull/10
  • https://github.com/istqborg/istqb-ct-atlas/pull/2
  • https://github.com/istqborg/istqb-ct-tas/pull/7
  • https://github.com/istqborg/istqb-ct-tae/pull/9
  • Convert Business Outcomes to the new markup istqb_product_template#17
  • https://github.com/istqborg/istqb-ctfl/pull/18
• Translate headers "Code" and "Name" for Business Outcomes, see e.g. document syllabus-de.tex from istqb-ct-tas.
• Add a schema for files traceability-matrix.yml that specify a Traceability Matrix between Learning Objectives and Business Outcomes and add an example file traceability-matrix.yml for the example document.
• Add snippet istqb/common/traceability-matrix that processes traceability-matrix.yml.
• Update snippet istqb/common/traceability-matrix, so that it also typesets an appendix with a Traceability Matrix Table.
• Update snippet istqb/common/traceability-matrix, so that it also typesets the full Traceability Matrix Table.
• Demonstrate the snippet istqb/common/traceability-matrix on the example document.

This PR also makes the following changes:

• Add argument --preview-continuous to command compile-tex-to-pdf:

  usage: template.py compile-tex-to-pdf [-h] [-pvc]
  
  options:
    -h, --help            show this help message and exit
    -pvc, --previous-continuous
                          Keep recompiling the TeX files as they change
  

  This enables the interactive continuous compilation of TeX files.

• Support partial recompilation with the compile-tex-to-pdf command.

• Remove tabs from the source code.

Closes #61.

[danopolan]

good progress so far

[Witiko]

@danopolan For your review, please see my demo in #61 (comment).