More self-evident icon to access the edit message dialog

[Moin]

@chapoi

I also moved it over to the right, to join the other icons. Felt like better placement

I understand that in the context of RTE, but in markdown mode with a preview on the right, my typing activity happens on the left, so the button now feels quite far away. Having it next to the language selector made more sense to me than having it next to the close button.