Dynamic column width in two column mode

**Is your feature request related to a problem? Please describe.**
I use `two column mode` exclusively with my desktop browser.
The left column has a _mostly_ fixed width. You can't change it manually to for example see more posts on screen or make it less _crumbed_.

**Describe the solution you'd like**
Make the left (main) column resizable, preferably a simple resize with the mouse by grabbing the space between the columns.

We briefly talked about this in the comment section of the initial release of the `two column mode` any you said this is something you thought about. That was several month ago and since it is not a thing yet I thought it might be a good idea to create a feature request.