Add note if integrity check is disabled

Our issue template states that users should post the output of `/index.php/settings/integrity/failed`, at the moment it displays that all passes have been passed if the integrity checker has been disabled.

This is however a wrong approach considering that some distributions are gonna package Frankenstein releases and makes it harder for us to detect such issues. Thus if the integrity code checker is disabled (using the config switch)  it displays now: `Appcode checker has been disabled. Integrity cannot be verified.`

This is not displayed anywhere else in the UI except these URL used for us for debugging purposes.