Display available categories with option to add additional categories

[himanshub16]

• A function to get available categories for blog has been made available in this commit.

• This is to be reflected on index.html page.

• Also, there should be option to add categories if not available.

• For reference, you can see how Stack Exchange implements adding tags http://stackoverflow.com/questions/ask

[gauthamzz]

this requires adding a new category on categories section also

[himanshub16]

The author can just submit the post. These changes could be made by the blog admin. Such moderation can help avoid ambiguous categories.

[gauthamzz]

i think we should mention that categories available in the default text field of the editor

[himanshub16]

This commit added the feature to fetch the categories. It has to be integrated with the editor. I'll try when I get time. Uploaded this so that someone else could continue the work.