Update core/components/formit/elements/snippets/snippet.formitischecked.php

Now receives multiple values in JSON rather than as a comma-delimited list (fixes bug fix when commas were present in values)
Update core/components/formit/elements/snippets/snippet.formitisselected.php

Now receives multiple values in JSON rather than as a comma-delimited list (fixes bug fix when commas were present in values)
Update core/components/formit/model/formit/firequest.class.php

Now uses JSON to store multi-value arrays, rather than comma-delimited string. (Fixes a bug when commas were present in values)
Also tweaked convertMODXTags() to allow the JSON to work correctly.
Update core/components/formit/elements/snippets/snippet.formitretriever.php

Fixes bug with checkboxes, multi-selects etc. 
[#9457] Fixed issue with commas in values causing errors with FormItIsChecked & FormItIsSelected