Add support for rcloud.params in mini mode

[useless5771]

@gordonwoodhull, this is an initial proposal of the solution for supporting rcloud.params in MINI mode.

Please note that just the last commit is relevant, all commits before it are changes included in PR https://github.com/att/rcloud.params/pull/14

Essentially the solution involves:

• turning off cell result processing queue synchronization, as this context is not available in mini mode
• introducing specialisations of rcw.set, rcw.append and rcw.prepend functions that invoke a wait callback function associated with paramSet form right after the element got pushed to the front-end. This enforces consistent behaviour between edit and mini modes. (without this, users would need to explicitly invoke paramSet wait function)

The new functions are named rcw.*.paramSet so they appear with the related functions from rcloud.web. This isn't ideal though...

A possible improvement would be to make the rcw.* functions S3 methods, then we could provide different implementations for specific classes, e.g. shiny.tag, paramSet...

rcw.* functions take as the first argument a jquery selector, not element that should be displayed, e.g.:

rcw.set <- function(selector, what)

It is possible however to specify which argument of a function should be used for method dispatch in R so we should be able to migrate rcw.* functions to methods without having to change the functions' signatures.

[gordonwoodhull]

Thanks Mats - this is merged. I'm calling it "0.8" because it's getting close to releasable.

Simon and I will clean up the interface and the other mess in rcloud.web that this exposed.