Thank you so much for the reply. It took me the whole week to properly understand it, but in the end all it took was 15 minutes last night to get it to work and an hour today to get it working right. 
Here is the commit where I implemented this. I made the rotation to be multiplied into the matrix immediately after the input is received. For some reason I had to switch x and y in the glRotate call.
Here is the commit where I implemented this. I made the rotation to be multiplied into the matrix immediately after the input is received. For some reason I had to switch x and y in the glRotate call.