[FIX] *: fix some side-effects of...

[FIX] *: fix some side-effects of https://github.com/odoo/odoo/commit/9de1bc0eef6f5bfaa2a8d745431caa361ae91548

- JS Modals were not correctly built anymore, their .modal-body element
  was duplicated and many without-effect JS lines were introduced (as a
  side effect, the form view design was broken when inside modals)

- Tests were changed to make bugs go unnoticed. For example, the media
  dialog functionnality was entirely broken because the .modal-dialog
  element was not receiving the correct class anymore.

- The JS translation function is _t, not _

- Do not use the <title/> tag as a regular DOM element, it is meant to
  be unique, in the <head/> section

- CSS rules were added to the utils.scss file, which is meant to contain
  functions and mixins, otherwise, the rule is duplicated in every asset

- Some icons were still broken, as missed by https://github.com/odoo/odoo/commit/f90cf060a3cfeb37a67bec83264c0aaab8892b56

- Tests were changed to use [role="dialog"]/footer/header in their
  selectors without any reason, this commit restores some of that to
  avoid rebase conflicts with the BS4 work.

- ...

Note: other elements should still be discussed, like the direct use of
the 'o_form_label' class in views definition... but those do not cause
direct problems.