i18n fixes (#1614)

* i18n fixes

- fix issue with default (fallback) language set to browser language
- fix issue with fallback language loading when browser language set to
non-English locale

* code and UI fixes

- move document list i18n strings into own scope
- replace MDL menu with @angular/material menu (fixes issue with menu
items translation, not supported by MDL)
- minor improvements

* fix unit tests

* improve i18n docs and code

- provide basic documentation for Translation service
- remove custom Login component localisation in favour of documentation
sample
- simplified i18n setup for demo shell (single path for dev/prod env)

* remove unnecessary comments

demo-shell-ng2/app/app.component.html

@@ -39,14 +39,14 @@
                 <span class="flag-icon flag-icon-gb"></span>
                 <label tabindex="0"> English</label>
             </a>
-            <a class="mdl-navigation__link" (click)="changeLanguage('gr')">
-                <span class="flag-icon flag-icon-gr"></span>
-                <label tabindex="0"> Greek</label>
-            </a>
             <a class="mdl-navigation__link" (click)="changeLanguage('it')">
                 <span class="flag-icon flag-icon-it"></span>
                 <label tabindex="0"> Italian</label>
             </a>
+            <a class="mdl-navigation__link" (click)="changeLanguage('ru')">
+                <span class="flag-icon flag-icon-ru"></span>
+                <label tabindex="0"> Russian</label>
+            </a>
         </nav>
         <span class="mdl-layout-title">Components</span>
         <nav class="mdl-navigation">