### 1) Refresh Token & Cron

Intervat API's provide use both access & refresh tokens. As long as
we keep a valid refresh token, we can keep the connection opened by
requesting a new refresh token.

Currently, we force the connection to close after 4 hours, but it's
too short.

This commit goes to the opposite way, and keep the connection opened
as long as the user wants.

As we need to keep a valid refresh token, we add a cron who execute once each 2 days
to fetch new refresh tokens.

Also, to prevent being stuck, add a new button in res settings to
manually close the connection.

### 2) Accounting firm

When submitting vat return to Intervat API, we have 2 situations:
1. The user submit his own declaration
2. An accounting firm submit the declaration for the client

The current implementation works nicely with situation 1, but not 2. The problem is
when starting the authentication proccess, we give Intervat a company number, the current
company number. But when an accounting firm is set on the company, we should use the
VAT number of the firm instead of the current company, as it will be an accountant from
the accounting firm who will submit the return.

So this commit try to find the accounting firm VAT before the current company VAT for
the authentication proccess. Also, add a new settings in Intervat settings to change the
accounting firm from there.

### 3) Small fixes

Small fixes done for corner cases, see commits messages.

task-5420287,5500052,5495079