new Composer tab

[Alex Heneveld <al...@cloudsoftcorp.com>]

Hi AlexZ, and Brooklyners-

AlexZ has been working on better blueprint editor support, in part in 
#865.  This is currently blocked because the
"application-add-wizard" doesn't play nicely with CodeMirror.  (The 
wizard impl tries to copy HTML elements, but
CodeMirror only binds to one of them, I think, or something like that!)

Having chatted about it we think the YAML editor doesn't fit in this 
wizard at all.  We propose a new top-level Composer tab.

This should simplify #930 also.

Details below:

* add app wizard is *only* for catalog; the tab where you add yaml (and 
the little-used "others") will be removed
     * you still have an optional "preview" step which a user can visit 
after the "friendly" set-config step (step 2)
         * it has options to "Edit in Composer" or "Deploy Now"
     * for "template" items which currently render as yaml as in step 2 
(e.g. if it includes a location)
         it doesn't make sense to show the set-config and the usual path 
is to go to composer;
         * in step 2 instead of set-config, we show the "preview" tab, 
again with "edit in composer" and "deploy now" as buttons
             * and a wee banner at the top saying "this item is a 
template; it is recommended to [edit in composer]" or similar
             * in time, validate the blueprint and disable "deploy now" 
if e.g. location is called "change me!"
                 (or better, evolve how we deal with templates)
* there is a new top-level "Composer" tab shown between Applications and 
Catalog
     * this is where you write yaml
     * buttons to "add to catalog" and "deploy now"
     * soon this will support drag-and-drop, a graphical view of apps, 
and a palette (what AZ is working on)
     * we might also have other tabs a la Swagger Hub which show the 
documentation
         e.g. config keys, sensors, effectors, in a pretty way
     * NB: there are actually two modes supported here, writing apps and 
adding to catalog;
         while it is supported to add to catalog by passing a normal 
blueprint,
         the catalog.bom syntax has more options and so -- in time -- 
the edit experience should
         become more sophisticated for adding to catalog, e.g. defining 
catalog metadata, tests, etc
* the "Catalog" tab need no longer support writing YAML there, as we 
have the composer;
     * if someone clicks "YAML" after + here, they are taken to 
composer; they can add to catalog from there
     * soon after, we improve that experience, maybe by making locations 
easier to define in the composer,
         and by supported edits to an existing catalog item, and 
automatically suggesting the version to save as
         (same version if it is SNAPSHOT, or minor version bump with 
SNAPSHOT added otherwise)
     * we'd also like a way in the UI to apply a blueprint version 
upgrade to running entity/application instances
         (we have this in the backend but not in the REST API support); 
being able to edit-and-apply via the composer
         could be quite cool, e.g. if you are adding new effectors etc 
(in time, not immediate!)
     * NB:  it might also be useful to have a "diff" view for catalog to 
see what changes between versions,
         e.g. if someone is thinking of applying a version update they 
can "preview changes"

Best
AlexH

[1] https://github.com/apache/incubator-brooklyn/pull/865