Keep aspect ratio of images if width or height is not known

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>

[REF]main.py: fix generated VALUE formula in `__prepare_calc_formulas` function

Approved-by: stephane_bidoul <stephane.bidoul@acsone.eu>

If the Genshi expressions generates a number value (float or integer),
the generated formula will be `=VALUE("1.1")` which is problematic if the
user machine is configured to use a decimal separator different than the `.`.
With this fix the generated formula will be `=VALUE(1.1)` (without the quotes)
which is correctly handled with by the `.ods` format.

Improve error message 'We handle urls in tables or text paragraph only'

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>

Add multiline format function

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>

Support text:span in functions

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>
Approved-by: Alexis de Lattre <alexis@via.ecp.fr>

[FIX] Always process manifest file at the end of the process since its content depends on others filers"

[FEA] Add image injection twice test

      different names, using the order parameter

fixed wrong type conversion for numeric variables.

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>
Approved-by: Alexis de Lattre <alexis@via.ecp.fr>