Rename condition to comment in base_condition_template

The texts are not conditions, this name was a bad choice.
Rename Conditions to Comments in invoice_condition_template
Move the comments fields in a page

They take too much place in the first page of the notebook.  Improved the
layout of these fields (use the same layout than sale_condition_template)
Update translations
Rename base_condition_template to base_comment_template
Change occurrences of base_condition_template to base_comment_template
Rename invoice_condition_template to invoice_comment_template
Replace occurrences of invoice_condition_template to invoice_comment_template
Rename models and remaining occurrences from condition to comment
Rename the pot files
Merge pull request #17 from guewen/8.0-invoice_condition_template-better-ui

Rename invoice_condition_template and improve its UI