display difficulty level icon in the website

**Details**

Added the difficulty icon next to the problem name in the blog post

**Notes**

Difficulty icon is similar this:

![image](https://user-images.githubusercontent.com/32248549/123884580-69038d80-d900-11eb-9773-27184daefb67.png)

**Expected behavior**

![image](https://user-images.githubusercontent.com/32248549/123884795-ec24e380-d900-11eb-9eea-12ca14b93ea9.png)

