refractor: shell (#287)

* Refractor components.
* Shift theme picker component to shared module.
* Shift progress bar service into its own folder.
* Add footer to app shell.
* Replace mat-icon by font-awesome icons.
* Fix sidenav visibility bug for handsets.
* Add comments.

Closes #286, Fixes #285

src/app/shared/language-selector/language-selector.component.ts

@@ -3,7 +3,7 @@ import { Component, OnInit } from '@angular/core';
 import { FormControl } from '@angular/forms';
 
 /** Custom Services */
-import { I18nService } from 'app/core';
+import { I18nService } from '../../core/i18n.service';
 
 /**
  * Language selector component.