[FIX] web_editor: adapt col size to avoid too small select

We should avoid col-md-3 in col-md-9 as the menu dialog is instanciated at 2
places:
  - When creating a link in the editor
  - When editing website navbar menu

In the second case, there is a hack in `content.js` to remove `modal-lg`
lowering the width of the modal and making the select too small.

[FIX] website: lower navbar font size

With BS4, font-size of navbar element went from 13px to ~17px (rem unit
computation).

14px seems better than previous 13px as the frontend content size is
higher than the backend one. Thus, 13px looks too small in contrast with the
frontend page content.

[FIX] website_crm_partner_assign, website_customer, website_membership: fix layout

This commit fixes multiple layout issues, mainly by aligning code of the 3
modules:
  - Add margin right to avoid text to be against image
  - Using image_medium everywhere
  - Fixing search input width

publish toggle red + odoo primary is weird -> gray
navbar now has a background & float-right not working since flex
-> remove navbar class, use d-flex and ml-auto so the right element will be floating since using all available width

task-1878150