[PURR][#2814]Knowledge base component home view and searching result user interface change

[kuang5]

PURR Ticket: https://purr.purdue.edu/support/ticket/2814

We wanted to update the user interface of the knowledge base home page and the searching result page to include:

1. On knowledge base home view (such as https://purr.purdue.edu/kb), display the Categories list on the left pane for navigation, and display the articles on the right pane. Same applied on category article view (such as https://purr.purdue.edu/kb/aboutpurr?sort=recent) and searching result view.

2. When a searching for articles is done, display the matched articles by its category. Under the article title, display the excerpt from the article that includes the searching term. This helps user quickly locate the article that is wanted.

Issues found and fixed in com_kb\site\controllers\articles.php:
path of Category model instance $category is not set, which causes the section parameter is not set in the $category method link() and the sort link won't work as expected.

Test steps:

1. Access https://dev.purr.purdue.edu/kb, which should display the category menu on the left pane and articles on the right pane. Same layout can be found on the category page such as https://dev.purr.purdue.edu/kb/aboutpurr.
2. Enter "doi" in the searching text field and click on the Search button. The searching result should be displayed by its category such as Data Publication, PURR Access & Use and so on. Click the Popularity or Recent button the results will be sorted by the corresponding. Each article includes the title, excerpt with the searching term highlighted, and the last modified date time. Choosing and clicking one category menu item on the left pane, such as About PURR, a new search is performed and the articles in About PURR category only should display. If no result is found, it won't show anything.

Test is done on dev PURR and it works as expected.