Draft: Read previous datetime from env

Related to management#821 (closed)

Reimplement incremental mode reading "FROM_DATETIME" env variable instead of opening the previous table of contents XML file in Git.

TODO before merging

• restore .gitlab-ci.yml

.vscode/extensions.json

+{
+  // See https://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
+  // Extension identifier format: ${publisher}.${name}. Example: vscode.csharp
+
+  // List of extensions which should be recommended for users of this workspace.
+  "recommendations": ["ms-python.python", "brainfit.vscode-importmagic"],
+  // List of extensions recommended by VS Code that should not be recommended for users of this workspace.
+  "unwantedRecommendations": []
+}