Attempt to add authorization to endorsement API

[vickyc2266]

Attempted to resolve #26

Attempted to debug the ability for authentication with the endorsement feature of posts. Found that a potential reason for the test failure for the endorse posts feature could be because of undefined uid throughout different files that have to do with the endorsement feature in files such as src/socket.io/posts/tools.js, src/api/posts.js, test/helpers/index.js, test/socket.io.js, and etc

The following files were gone through and edited:
src/api/posts.js
src/posts/endorsement.js
src/privileges/posts.js
src/socket.io/posts/tools.js
test/helpers/index.js
test/posts.js
test/socket.io.js

[evelynnchen-cmu]

Due to implementation not working 100% and incoming merge conflicts, we will not be accepting this pull request.