Show the placeholder image in the "edit file" dialog (see #7032)

Show the placeholder image in the "edit file" dialog if the original image exceeds the maximum dimensions supported by the GD library.
Also apply the font settings to the ACE element (see #7103)

This is just the fix for the unsynchronized cursor problem. There is an ongoing discussion on changing the font-family, which might be changed in the future.
Replace insert tags in external redirect targets (see #6765)
Merge branch 'hotfix/3.2.12' into hotfix/3.3.3

Conflicts:
	system/docs/CHANGELOG.md
	system/themes/default/main.css