improve: lazy resolver (#4253)

* default to empty `ImmutableMap` when grabbing op metadata
* pass `errors` into JsonSchema components
* Account for Immutable data structure in JavaScriptonSchema...
...and create empty Lists instead of Maps by default.
* Pass ImmutableList through to JsonSchema child components
* Add lazy resolving spec state extensions
* TEMPORARY: disable conventional resolved spec
* WIP
* Use resolveSubtree in Operation display
* Freebie: short-circuit Markdown component if it is given plaintext
* NEW DEFAULT BEHAVIOR: `defaultModelsExpandDepth: 1` does not expand individual models
* Render faked Model expander to trigger resolution
* Baseline support for Editor lifecycles
* Display operation summaries before the operation is resolved
* Test migrations
* WIP
* Swagger2 TIO Body params
* a bit of cleanup
* Debounce string param inputs
* Reach into unresolved operation for deprecated flag, if available
* Fire subtree request outside of render
* Remove debugging flags
* Fix logical errors in spec statePlugins
* TODOs become TODONEs!
* Migrate deeplinking feature to non-resolved spec action
* ESLint fixes
* Reduce action dispatch volume; run resolver on next tick
* Batch resolver requests; use batch progressive results in later iterations
* Add loading states to Model and Operation views
* Preserve object order; remove dupl. import; add warning for action
* LINTER!
* Use require to load SVG
       Works around Webpack weirdness

src/img/rolling-load.svg

@@ -0,0 +1 @@
+<svg width="200px"  height="200px"  xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="xMidYMid" class="lds-rolling" style="background-image: none; background-position: initial initial; background-repeat: initial initial;"><circle cx="50" cy="50" fill="none" ng-attr-stroke="{{config.color}}" ng-attr-stroke-width="{{config.width}}" ng-attr-r="{{config.radius}}" ng-attr-stroke-dasharray="{{config.dasharray}}" stroke="#555555" stroke-width="10" r="35" stroke-dasharray="164.93361431346415 56.97787143782138"><animateTransform attributeName="transform" type="rotate" calcMode="linear" values="0 50 50;360 50 50" keyTimes="0;1" dur="1s" begin="0s" repeatCount="indefinite"></animateTransform></circle></svg>