security: Fix some reported security issues

[laf]

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Introduce two new functions to help clean up user input + displaying it.

A big thank you for the two responsible disclosure reports we've had.

Jaspher Respicio (Twitter: @Jaspher):

• XSS within the dashboard widget titles and notes widget.
• XSS from port descriptions, this could be triggered by updating interface descriptions directly on the devices or via the override within the WebUI.

Fatih Acar (gandi.net):

• Pre-auth SQL injection vulnerability using the default MySQL auth (other auth modules unaffected).
• Remote command execution using netcmd.php

[scrutinizer-notifier]

The inspection completed: 2 updated code elements