BC3 files importer

This module adds a way to bring construction budgets in the Spanish BC3 file format into Odoo as sales quotations, instead of typing every line by hand.

Where it appears: - A new BC3 menu with entries for BC3 Versions, BC3 Quotations, BC3 Orders and Import BC3. - A BC3 menu inside the Sales app. - A button/action that opens the import wizard, where you upload the file and choose a customer, a project, a BC3 version, an optional default product and whether missing products should be created.

What happens when you import: - The file is read, its character set is detected automatically, and each record is interpreted using the rules of the selected BC3 version. - A new quotation is created and filled with the budget lines; sections and notes are kept as section and note lines. - Measurement records (the detail of quantities, lengths, widths, heights) are appended as text under the matching line. - Products are matched by their internal reference; if none is found and the option is ticked, a new product is created, otherwise a generic unit product is used. - Units of measure such as m3, m2 and units are recognised, and the quotation is marked as a BC3 quotation.

Business rules and data: - Each BC3 version must have unique register names, otherwise Odoo blocks the save. - Rules map file fields to quotation, quotation line or product fields, and can be marked as primary key or child. - Quotations store BC3 header information: program, version, date, comment, certification number and date, and base URL. Quotation lines store the BC3 code.