Completed the todo - Divided the constants.js of redux into submodules

[Vishawdeep-Singh]

Completed TODO at the top of constants.js

Changes: I created a folder called “constants” and sub-modules of Redux constants, such as “fileActions.js”, “errorActions.js”, and so on. I then imported these sub-modules into the original “constants.js” file, spread them, and exported them.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123