title: importing components in ngx-bootstrap throws 'not a known element' error
body: <p>I imported the datepicker and it shows up fine.</p>
  
  <p>But when I try to import a typeahead or buttons or anything, I get the <code>&lt;whatever&gt; is not a known element</code> error.</p>
  
  <p>What I'm doing is import the module in the <code>app.module</code> like that:</p>
  
  <pre><code>import {DatepickerModule} from 'ngx-bootstrap/datepicker';
  import { TypeaheadModule } from 'ngx-bootstrap/typeahead';
  import { ButtonsModule } from 'ngx-bootstrap/buttons';
  // also tried:
  // import { DatepickerModule, TypeaheadModule... } from 'ngx-bootstrap';
  // ..but again no luck
  ...
  imports: [
     DatepickerModule.forRoot(), //only this works 
     TypeaheadModule.forRoot(),
     ButtonsModule.forRoot(),
     ...]
  </code></pre>
  
  <p>Then on my <code>history.module</code> in a same way with the only difference that <code>.forRoot()</code> is now omitted.</p>
  
  <p>Then on a child component of the parent history component I have:</p>
  
  <pre><code>&lt;span *ngIf="showFilters" class="value bootstrap-iso" &gt;
    &lt;div style="display:inline-block;"&gt;
      &lt;datepicker
        [(ngModel)]="dt"
        [datepickerMode]="'month'"
        [showWeeks]="false"
        [dateDisabled]="dateDisabled"
        [maxDate]="today"&gt;
      &lt;/datepicker&gt; 
    &lt;/div&gt;
  &lt;/span&gt;
  </code></pre>
  
  <p>which works, but for example these don't work:</p>
  
  <pre><code>&lt;typeahead [typeahead]="'documents'"&gt;&lt;/typeahead&gt;  
  &lt;btnCheckbox&gt;&lt;/btnCheckbox&gt;
  </code></pre>
  
  <p>Doesn't matter if I include <code>ngModel</code> or other attributes, I always get the not a known element error. So I assume it has to do with my imports, my naming, or somethng, but honestly I can't see what's missing.</p>
  
  <p>EDIT: Using Angular 4, <code>"@angular/cli": "1.1.1",</code> <code>"ngx-bootstrap": "^1.7.1",</code> <code>"bootstrap": "^4.0.0-alpha.6",</code> <code>"typescript": "~2.3.3"</code></p>