Rename partnership concepts

[inulty-dfe]

Context

Label	Meaning
Providers	All providers
Training provider	A provider that runs ITT training courses
Accredited provider	A provider that is accredited by DfE
Training partner	The training provider in a provider partnership association
Accredited partner	The accredited provider in a provider partnership association
Ratifying provider	The Accredited partner that ratifies the course of a Training partner

The wording in specs still needs to be changed.
For example

  scenario 'i can edit accredited providers on the index page' do

Needs to change to accredited partners. This is WIP until all the wording is updated.

Changes proposed in this pull request

Update all the UI labels and text to accurately convey the concepts above.

Guidance to review

Accredited partners V Accredited partnerships

[inulty-dfe]

Trello https://trello.com/c/kkQag5QG/338-tech-debt-rename-partnership-concepts