Browser desyncs state on any browser navigation

[mathmods]

Describe the bug
Using the back or forward navigation button in the browser will desync the state.
If you want to go back, the history gets sent 2 steps back.
If you want to go forward, you get sent back.

To Reproduce
Steps to reproduce the bug:

1. Go to the staging site
2. Enter any lesson with more than 1 practice (for example lesson 6)
3. Enter any practice
4. Navigate to any new practice
5. Use the browser back button (and notice the history getting popped twice)
6. Use the browser forward button (and get sent back)

Expected behavior
The back button will only pop history once.
The forward button will either do nothing or navigate the user to the requested resource.

Information about your device (please complete the following information):

• Operating System: Chrome (latest stable)
• Browser: Windows

Additional context
Discovered while testing #277. Apparently the current setup is that on any popstate the browser will navigate back, but this also triggers a popstate from the navigate back function. (Thus making the browser think it's gone back another time.)
Popstate also triggers on any change in the link, even when it's supposed to go forward. Thus activating the navigate back function.