Adds the concept of projects

See merge request !76

Replace the FK towards Document on OcrModel by a M2M relation

Closes #353

See merge request !77

#339 - Update DiploPanel.vue _ copying-empty-lines-in-panel-4-should-insert-cr

See merge request !73

Create .../models/\d+ with parents, preventing an error message at start of training

See merge request !75

up to the model_s_ directory.

Change in pyvips calls in order to prevent memory leak

See merge request !74

Moves the CUSTOM_HOME env variable to the variables.env file to fix a compose file merging confusion.