359 post page revamp v1

[AjobK]

closes #359

What is it supposed to do
Revamped post edit with cancel functionalities

How can we test your branch
Create a post, edit banners, do all kinds of things.

Additional notes
We use an UNSAFE method (willReceiveProps), but this is very thought through.

1. General checklist

• [x] a. Tested happy flow.
• [x] b. Tested unhappy flow.
• [x] c. No unexpected exceptions.
• [x] d. No code with high complexity. (Big O)
• [x] e. EOF newline.
• [x] f. No linter warnings or errors.

2. If relevant, front-end checklist

• [x] a. Responsive. (Desktop all the way to mobile 320px)
• [x] b. Using SCSS variables where relevant.
• [x] c. Relevant class names
• [x] d. No modified global SCSS properties, except if necessary and fully tested the impact.
• [x] e. Checked caniuse for more modern CSS properties.

3. If relevant, back-end checklist

• [x] a. No unhandled promise rejections.
• [x] b. Seeders still functional.
• [x] c. No primary-key violations.
• [x] d. Normalization, at least 3NF.
• [x] e. Used guards (middleware) where necessary and tested if route is guarded.

4. If relevant, test these browsers

• [x] a. Chrome
• [x] b. Firefox
• [x] c. Opera
• [x] d. Edge
• [ ] e. Safari

---

PR Rules
1. Add relevant labels.
2. Select at least two reviewers.
3. Assign all reviewers allowed to merge the branch, including yourself.
4. If relevant to the sprint, put related issue in 'Awaiting Approval' column on project board.
5. Add to the corresponding milestone.

Reviewer info
1. You can use aliases to refer to specific PR checklist items. For example 'Hey @JohnDoe, for this line please check 3.a and 1.d.'
2. Where possible, please use the suggestions feature in github so the author has a better idea of the solution you had in mind.

This form should be filled in by the author of this PR.