Tidier way of inserting "Ma Says" and inline callouts

While looking at customising input sanitisation I came across [this](https://github.com/publify/publify/wiki/how-to-create-your-own-typo-macro-filters) help page.

Using this we're now able to insert the "Ma Says" snippet using something like so:

    <publify:masays url="https://www.moneyadviceservice.org.uk/en/campaigns/saving-for-a-holiday">
        Saving for a Holiday
    </publify:masays>

You still need to switch to the source view to add this, though possibly someone with better knowledge of CKEditor might know how to whitelist our custom tags.