Move acquisition.instrument DB column to a "free column"

[grololo06]

Follow-up of #264.
For each project, add a free acquisition column in the acquisition-level mappings (column projects.mappingacq).
Copy acquisition.instrument existing data into this new free column.
Unfortunately, for existing production data, 2 lines have their "free columns" taken entirely, meaning we'd need to add a t31, to be sure to cover all cases.
The project-level mappings are plain text, meaning a specific parsing is needed to ensure correct compatibility with back-end. Python in PG?

[grololo06]

Corresponding mapping will also be to remove in import code.

[jiho]

Regarding this

Unfortunately, for existing production data, 2 lines have their "free columns" taken entirely, meaning we'd need to add a t31, to be sure to cover all cases.

The amount of free columns could also be increased to 60 in anticipation of merging acq and process. Also, 30 appeared to be limiting in some cases in the past.