Add line height as a setting

[mattpass]

Add line height as a setting in the Style section. All themes have had the set line heights removed so we can now apply a line height to any theme really.

It is applied to the theme class selector, eg:

.cm-s-solarized {
  line-height: 1.5em;
}

[mattpass]

Update: Can actually set on editor.php line 59.