Editor has large margins when text is too long

Problem/Motivation

When entering json into the Code mirror editor and the code is too long the edit view box becomes too wide and the text is thrown offscreen.

Steps to reproduce

After installing Code mirror create a new text format and set the editor to only use Code Mirror. Then enter a json string that is very long(I'm using one that's 68 lines long) and save the node. When entering the edit view again you will notice the div now has massive margins.

Proposed resolution

Update the CSS so the editor always stays on the left no matter how much text is on screen.

Remaining tasks

User interface changes

API changes

Data model changes