Break the lib index file into separate files for the major parts of the flow

[brafdlog]

Original comment:
I want to remove all the code from the root index.ts, to get a clear list about what the backend exporting. I have three (or more) points:

Move all the code from index.ts to separate files in a logical order. The export functionality should be in its file, the same with the import functionality, and the method that takes from import to export in another file.
In this way, we can validate (I hope there is lint for that) the Vue access only to the @/originalBudgetTrackingApp, and the backend itself access only to the flow module, and this module uses its "internal" methods to import and export.
With this structure you can understand half of the code only by its module.