Resolve "Enhance Workflow of leaving editions"

What does this mr do?

Read #545 (closed) for desc

Changes

• clicking back if you unenrol does not lead to access denied as the last page the user was on was the edition page anyway. This, however, does not solve the user being on the /modules or the /participants subcontent page and clicking unenrol. However, the probability of this happening is lower. Furthermore, it's not very important.
• the unenrol button is now disabled properly by using a fake button.
• A new dialog was introduced to leave an edition in place of the old page redirect.

Screenshots

Dialog

Fake button

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #545 (closed)