Improve columns management in Excel

[Guts]

Stakes:

• 1 metadata attribute = 1 column: depends on the metadata type (different worksheet)
• 1 column = 1 title: needs to be translated
• 1 column = 1 dimension (width and height)
• 1 column = format

In the older versions, columns names and row were managed with big dictionaries stored into the isogeo2xlsx.py file.

With c05f3e720b70274c84c56143140aaa5f3000a7d4 columns/attributes were moved to independant modules.

It could be improved with storing the columns titles and dimensions into these modules.