Cannot set session options using REST API / Web UI

Some commands are configured using session options that you set using the `SET` command.  However, the `SET` command is not useful in the Web UI and REST API because the options you set are not preserved in the next request.  For example, when using CREATE TABLE AS you must `SET store.format csv` to set the output format to comma-separated value, but this is not possible via the REST API.

I propose that the API be updated to support options that are normally provided using SET:

1. The JSON API accepts an object "options" whose keys are options and values are option values.  The values should have an appropriate type for the given option, e.g. JSON boolean if the option type is boolean
2. The form-based API used by the Web UI scans any provided form fields that match a valid session option and sets those options, parsing strings according to the type of option