title: Nebular throwing 'Nb-action' is not a known element:' error?
body: <p>I am trying to implement nebular in my work so I am following <a href="https://akveo.github.io/nebular/docs/components/layout/overview#nblayoutcolumncomponent" rel="nofollow noreferrer">this</a> Nebular tutorial for work out.</p>
  
  <p>I have installed nebular. And it is working fine with <code>&lt;nb-layout&gt;</code> <code>&lt;nb-header&gt;</code> but when I am using <code>&lt;nb-actions&gt;</code> or <code>&lt;nb-menu&gt;</code> it is throwing the following error</p>
  
  <pre><code>compiler.js:1021 Uncaught Error: Template parse errors:
  'nb-action' is not a known element:
  1. If 'nb-action' is an Angular component, then verify that it is part of this module.
  2. If 'nb-action' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this 
  </code></pre>
  
  <p>I do not know what is the issue. How to fix it?</p>
  
  <p>side.html</p>
  
  <pre><code>&lt;nb-layout&gt;      
      &lt;nb-layout-header subheader&gt;
          &lt;nb-actions&gt;
          &lt;nb-action icon="nb-home"&gt;&lt;/nb-action&gt;
          &lt;nb-action icon="nb-search"&gt;&lt;/nb-action&gt;
          &lt;nb-action icon="nb-edit"&gt;&lt;/nb-action&gt;
          &lt;/nb-actions&gt;
      &lt;/nb-layout-header&gt;
  
  &lt;/nb-layout&gt;
  </code></pre>
  
  <p>side.ts  //component</p>
  
  <pre><code>import {Component} from '@angular/core';
  
  
  @Component({
      selector:"sidebar",
      templateUrl:"./side.html",
      styleUrls:["side.css"]
  })
  export class sideComponent{
  
  
  }
  </code></pre>
  
  <p>sbar.module.ts</p>
  
  <pre><code>import { NgModule } from '@angular/core';
  import { CommonModule } from '@angular/common';
  
  import { RouterModule,Routes } from '@angular/router';
  import { NbSidebarModule, NbLayoutModule, NbSidebarService } from '@nebular/theme';
  import {sideComponent} from "./sidecomp/side";
  
  const routes: Routes = [{path:"sidebar",component:sideComponent}]
  
  
  @NgModule({
    declarations:[
      sideComponent
    ],
    imports: [
      CommonModule,
      RouterModule.forRoot(routes, { useHash: true }),    
      NbSidebarModule,
      NbLayoutModule
  
    ],
    providers:[NbSidebarService],
    exports:[sideComponent]
  })
  export class SbarModule { }
  </code></pre>