Feature: Tags Support

[Manit1]

Fixes #18
Backend PR

[Manit1]

@abhishek97 Build works on my PC. I don't why the tests are failing! Please Help

[abhishek97]

@Manit1 After creating a new tag, i get the error:

• We don't allow deleting tags
• When adding tags to a question, the list is to be initially populated with some tags and not empty.

[abhishek97]

@Manit1 Also need to be able to search questions by tags. Need to make questions api changes
updated the issue with the required api

[Manit1]

@abhishek97 Done with the frontend fixes, now updating the backend.