Improve Email Alerts (high level ticket)

[TomSteinberg]

This needs to cover:

• [ ] 1 - Improving the experience of unsubscribing - #737
• [ ] 2 - Improving the experience of subscribing to an MP's updates from an MP page
• [ ] 3 - Improving the experience of subscribing for keyword alerts (get designers to suggest whole journey here)
• [x] 4 - Stop people subscribing to alerts based on postcodes actually being mentioned in parliament
• [x] 5 - Stop people subscribing to alerts based on when a person's name is mentioned in parliament
• [ ] 6 - Improve the experience of modifying a user's current email alerts (plural)
• [x] 7 - Improve the layout of the emails themselves #277 #251
• [ ] 8 - Improve the experience of signing people up to multiple keyword alerts #24

[struan]

Related: #737, #24, #284