title: ng2 smart table check boxes not persistent across all pages
body: <p>I'm new to ng2-smart-tables. I'm trying modify the example below from the GitHub page so that the check boxes don't disappear when moving from page to page.</p>
  
  <pre><code>import { Component } from '@angular/core';
  
  @Component({
    selector: 'basic-example-multi-select',
    template: `
      &lt;ng2-smart-table [settings]="settings" [source]="data"&gt;&lt;/ng2-smart-table&gt;
    `,
  })
  export class BasicExampleMultiSelectComponent {
  
    settings = {
      selectMode: 'multi',
      columns: {
        id: {
          title: 'ID',
        },
        name: {
          title: 'Full Name',
        },
        username: {
          title: 'User Name',
        },
        email: {
          title: 'Email',
        },
      },
    };
  
    data = [
      {
        id: 1,
        name: 'Leanne Graham',
        username: 'Bret',
        email: 'Sincere@april.biz',
      },
      {
        id: 2,
        name: 'Ervin Howell',
        username: 'Antonette',
        email: 'Shanna@melissa.tv',
      },
      {
        id: 3,
        name: 'Clementine Bauch',
        username: 'Samantha',
        email: 'Nathan@yesenia.net',
      },
      {
        id: 4,
        name: 'Patricia Lebsack',
        username: 'Karianne',
        email: 'Julianne.OConner@kory.org',
      },
      {
        id: 5,
        name: 'Chelsey Dietrich',
        username: 'Kamren',
        email: 'Lucio_Hettinger@annie.ca',
      },
      {
        id: 6,
        name: 'Mrs. Dennis Schulist',
        username: 'Leopoldo_Corkery',
        email: 'Karley_Dach@jasper.info',
      },
      {
        id: 7,
        name: 'Kurtis Weissnat',
        username: 'Elwyn.Skiles',
        email: 'Telly.Hoeger@billy.biz',
      },
      {
        id: 8,
        name: 'Nicholas Runolfsdottir V',
        username: 'Maxime_Nienow',
        email: 'Sherwood@rosamond.me',
      },
      {
        id: 9,
        name: 'Glenna Reichert',
        username: 'Delphine',
        email: 'Chaim_McDermott@dana.io',
      },
      {
        id: 10,
        name: 'Clementina DuBuque',
        username: 'Moriah.Stanton',
        email: 'Rey.Padberg@karina.biz',
      },
      {
        id: 11,
        name: 'Nicholas DuBuque',
        username: 'Nicholas.Stanton',
        email: 'Rey.Padberg@rosamond.biz',
      },
    ];
  }
  </code></pre>
  
  <p>This uses the selectMode : 'multi'option to show a column with check boxes. The check boxes do show, but every time I use the pagination links to go to another page, the selection is cleared. I'm trying to solve this problem because I have a problem on my project which is analogous to this.  </p>
  
  <p>I tried to find documentation on how to persist the selection across pages, but was not successful as only a limited amount of documentation is available.  This seems like a feature that's common enough that there should be more information on this out there, but doesn't seem to be the case.  Any help on this issue would be greatly appreciated.</p>