added Twitter and Facebook login

[abs8090]

This PR adds Twitter and Facebook login via the ParseAuthenticatable protocol.
The user of ParseTwitter or ParseFacebook still needs to implement TwitterKit or FBSDKCoreKit to obtain authentication keys and pass them to ParseTwitter.logn() or ParseFacebook.login() to authenticate with ParseServer.

[codecov]

Codecov Report

Merging #97 (c619c27) into main (403a02b) will increase coverage by 0.90%.
The diff coverage is 100.00%.

❗ Current head c619c27 differs from pull request most recent head 55d6b7d. Consider uploading reports for the commit 55d6b7d to get more accurate results

@@            Coverage Diff             @@
##             main      #97      +/-   ##
==========================================
+ Coverage   79.76%   80.66%   +0.90%     
==========================================
  Files          63       65       +2     
  Lines        5170     5411     +241     
==========================================
+ Hits         4124     4365     +241     
  Misses       1046     1046              

Impacted Files	Coverage Δ
...Swift/Authentication/3rd Party/ParseFacebook.swift	100.00% <100.00%> (ø)
...arseSwift/Authentication/3rd Party/ParseLDAP.swift	100.00% <100.00%> (ø)
...eSwift/Authentication/3rd Party/ParseTwitter.swift	100.00% <100.00%> (ø)

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[cbaker6]

Thanks @abs8090 for your contribution! I will look over soon.

In the mean time can you add an entry to the CHANGELOG.md file, something like (this should go right above ### 1.2.1):

__New features__
- Add ParseTwitter and ParseFacebook authentication ([#97](https://github.com/parse-community/Parse-Swift/pull/97)), thanks to [YOUR NAME](https://github.com/abs8090).

[cbaker6]

I updated your branch with the latest main, you should should pull your branch and then proceed with the rest of the changes

[cbaker6]

The PR is looking good! Be sure to "pull" your branch again before making anymore updates.

You had some inconsistencies in ParseTwitter with, twitterId, userId, and user. I switched them all to userId as it looks like that's what Twitter uses.

Things you need to do:

• Install SwiftLint from the contributors guide and fix the warnings.
• Verify you have all of the necessary keys for Facebook and Twitter and make sure your testcases are checking what they need to check

[cbaker6]

This looks ready to go!

Thanks for making your first contribution!