Use just a *model-parameters* special

Rather than a panoply of individual parameter specials...
Re-purpose existing model parameter specials
Add the model (a symbol) itself to model parameters
fixup
Lisp symbols to JSON and back
sym-suffix util function
Mode parameters parsed as sym => sym hash
db-name-string function

Needs a proper home.
Fix typo in transactions.lisp comments
Shadow :sequence
New model parameters with individual specials code

Neater and more extensible.  CLOS would be overkill, or so I keep
telling myself.
Backend changes for new model parameters
create-model changes for new model parameters
Query changes for new model parameters