Enable array support in mo templates

More info: https://github.com/tests-always-included/mo/tree/2.2.0#:\~:text=level%20of%20complexity.-,You%20must%20source%20mo,-.%20Look%20at

Needed for iwoca/modelling/platform/model-template#91.

Source mo and don't start new shells when calling mo. This way mo can read and process Bash arrays, which will enable the use of arrays in mo templates.

One drawback of this change though is that we won't process files in parallel any more, but AFAIK we don't process that many files in a single deployment and the processing of the files is fairly quick, so I don't think it would be that bad.