Made MD editor display a sandboxed iframe

[bookstack] / phpcs.xml

<?xml version="1.0"?>
<ruleset name="PHP_CodeSniffer">
    <description>The coding standard for BookStack.</description>
    <file>app</file>
    <exclude-pattern>*/migrations/*</exclude-pattern>
    <arg value="np"/>
    <rule ref="PSR2"/>
</ruleset>