Update Event categories and subcategories list

[bingzhang]

Description

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Fixes #(add issue number here and remove parentheses)

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[sandeep-ps]

Running the Mongodb import command will append new categories with previous categories.

@bingzhang, I think it's better to move this to db.py, and we need to replace the categories with the new categories. What do you think?

For the purpose of review, I will drop the local collection and add the new categories.

[sandeep-ps]

Please update the API specification file as the categories list is used in that too.

[bingzhang]

that is why I mentioned that in our technique meeting. I can work python code like what the current tag.json does.

[sandeep-ps]

Hi, @bingzhang, FYI, I'm updating this PR with README changes and potentially some minor code changes.