[8.0] port of module sale_condition_text -> sale_condition_template

port of sale_condition_template to v8.0

* rename account.condition_text to base.condition_template
* move fields in view to reflect document print
* rename type of field to position
* give better position names
* split module to be able to reuse conditions for purchase condition (used in https://github.com/OCA/purchase-reporting/tree/8.0/purchase_order_webkit_with_notes)
if this error is to be read by users, it should give a better message, if it is to be read by developers, it should rather be an assert