RFC fleshing out attachment_synchronize exports

[kevinkhao]

case: we need to import some files on an FTP server, run them through some process. Same for exporting some models from Odoo to the FTP server in a certain format

Basically, some kind of EDI-lite.

Currently, attachment_synchronize is adapted for our use case in import but there is limited exporting functionality.

Here is a module that we are about to use.

akretion/ak-odoo-incubator#268

Two things it helps organize:

• Exporting: we use mixins on our model, implement these methods and just call synchronize_export to have the formatted file generated and put on the backend
• Flag a model for exporting when some fields are modified on it

Functionality is currently a bit all over the place and not clearly delineated. Maybe someone has some ideas about how to better generalize or organize the code, functionality and module split.

Related issues and PRs:
akretion/ak-odoo-incubator#268
#2562
#2508

@florian-dacosta @bealdav