Added optional className param to JIcon constructor

Currently JIcons are initalized with a generated className based on
the name. This means all classNames are prepended with `jp-` but
this procludes the idea of extensions creating thier own JIcons
with project unique CSS selectors

packages/ui-components/src/icon/jlicon.tsx

@@ -117,9 +117,10 @@ export class JLIcon {
     JLIcon._debug = debug ?? !JLIcon._debug;
   }
 
-  constructor({ name, svgstr }: JLIcon.IOptions) {
+  constructor({ name, svgstr, className }: JLIcon.IOptions) {
     this.name = name;
-    this._className = Private.nameToClassName(name);
+    this._className =
+      className != undefined ? className : Private.nameToClassName(name);
     this.svgstr = svgstr;
 
     this.react = this._initReact();
@@ -351,6 +352,7 @@ export namespace JLIcon {
   export interface IOptions {
     name: string;
     svgstr: string;
+    className?: string;
   }
 
   /**