Added author_id to login response and methods to store and retrieve a…

[nluu175]

• Added author_id as a field to Reponse data on successful login.
• Added a methods to store and retrieve author_id to/from localStorage.

Expected behaviour:

• A new author_id field is stored in localStorage on successful login.
• author_id of the current user can be retrieved from the localStorage using getAuthorId that can be found in utils/localStorageUtils.ts

How to test:

• Check whether the author_id of the current logged in user has the same id with the one in database.

[kaynzhel]

lgtm, QA'ed with replacing one of the hardcoded AUTHOR_ID and it matches the uuid of the logged in user