Add configuration option for button image
Fix array_flip warning
Make icon file id an integer-field
Make upload location configurable
Rename config schema button icon field to button_icon_fid
Make file scheme also configurable
Merge pull request #91 from cs-shadow/icon-field

Make icon for embed buttons customizable
Merge remote-tracking branch 'upstream/8.x-1.x' into 8.x-1.x