Use monospaced font for CodeMirror editor.

Cursor position gets off with non-monospaced font.
STUD-1456.

Vertical alignment of monospace font in advanced settings via position css adjustment
XModule datadog metrics
Merge pull request #3163 from edx/christina/advanced-settings-font

Use monospaced font for CodeMirror editor.
Merge pull request #3164 from edx/flowerhack/better-xmodule-metrics

XModule datadog metrics
Initial implementation for api_manager app