Indicators api (#1837)

* [API] Added Indicators API

* [Indicators] Converted Follow Indicator to new Indicators API

* [Indicators] Converted URL Indicator to new Indicators API

* [Indicators] Changes to some legacy indicators for compatibility with new Indicators API

* [Indicators] Addressed code review items from https://github.com/nasa/openmct/pull/1837

* Updated tests for URL Indicator

* Adding Indicator API spec

* Address linting issues

* Switched to direct DOM manipulation rather than template compilation to avoid an unnecessary extra holder element

* Updated documentation to reflect changes to API

* Indicators api styling (#2076)

Updated styling for Indicators

* Update API TOC

* Fix color of items w-mct-example areas of Style Guide

Fixes #1837

* Status class refactoring and cleanups

Fixes #1837
- Significant cleanups and name refactoring to allow more
concise selector definitions, with changes in js, html and scss files;
- Updates in Style Guide > Status page, with some content
reorganization and clarification;

* Corrected out of date API

* de-zeptoed Indicator API test spec

* Remove promise from URLIndicator

* Separated legacy indicators support

* Updated Indicator specs to Jasmine 3

* Fixed checkstyle and lint issues

* Moved legacy indicators support to adapter folder

* Various fixes for Indicators

Fixes #1837
- Added SASS constants for Indicator colors;
- Removed commented code;
- Removed unused indicator classes from _messages.scss
- Fixed missing s-status-on class;

* Significant revisions to Style Guide Indicators content

Fixes #1837
- Better documentation including recommendations;
- Better and more concrete examples;

* Style Guide example tweaks

Fixes #1837

* Refinement to Style Guide Status and Limits content

Fixes #1837
- More detail and clarification on Status and Limits;

* Cleanup code

Fixes #1837
- Remove commented styles;
- Line return refinements;

platform/persistence/elastic/src/ElasticIndicator.js

@@ -32,11 +32,13 @@ define(
         var CONNECTED = {
                 text: "Connected",
                 glyphClass: "ok",
+                statusClass: "s-status-ok",
                 description: "Connected to the domain object database."
             },
             DISCONNECTED = {
                 text: "Disconnected",
                 glyphClass: "err",
+                statusClass: "s-status-caution",
                 description: "Unable to connect to the domain object database."
             },
             PENDING = {