Added base page for 'jottings'

Added base page for 'jottings', which are meant to be similar
to 'articles', except quick pieces.
    application/config/routes.php
    application/controllers/pages.php
    application/models/navbar_model.php
Added keywords/tags to sidebar

Added keywords/tags to sidebar
    application/views/sidebars/sb_article.php
Refactored keywords to common model

Refactored keywords to common model

    application/controllers/article.php
    application/controllers/pages.php
    application/models/article_model.php
    application/models/common_model.php   (+)