[Feature] Add localization support

[rpaschoal]

A couple of ideas on this:

• Every label and text visible to users must be customizable
• Support/Use Angular's i18n localization
• Refactor existing properties for placeholders to be passed as an Object to reduce the number of Input parameters and increase extensibility
• Must be released within a new minor version

This was brought on #37

[rpaschoal]

Work in progress and to be released in 1.0.8 (No need for a new minor version).

[rpaschoal]

Not adding i18n support right now as it seems that it only works on static text at the current version. It seems there is some work going on to add a i18n translation service as seen here https://github.com/angular/angular/issues/11405

Added a Localization interface so people can fully customize the text in this component. All future text will have a property in this interface. This will reduce the future size of Input parameters.

Added on #48

Example usage:

On your component's template:

<ng-chat [adapter]="adapter" [userId]="999" [localization]="myLocalization"></ng-chat>

On your component's class:

import { ChatAdapter, Localization } from 'ng-chat';

...

mylocalization: Localization = {
    title: 'Custom Title',
    searchPlaceholder: 'Custom Search Placeholder',
    messagePlaceholder: 'Custom Message Placeholder',
    statusDescription: {
      online: 'Custom Status Description',
      busy: 'Custom Status Description',
      away: 'Custom Status Description',
      offline: 'Custom Status Description'
    }
};

[rpaschoal]

Closing this as the related work was released on 1.0.8.