Updated getCurrentUser to use 4 different endpoints.

[cameronpcampbell]

Changed getCurrentUser to use 4 different endpoints to accommodate for the removal of the mobileapi/userinfo endpoint.

The function in this PR now uses:

• //users.roblox.com/v1/users/authenticated
• getPlayerThumbnail
• //economy.roblox.com/v1/user/currency
• //premiumfeatures.roblox.com/v1/users/{userId}/validate-membership

[alanbixby]

Thank you for the efforts however a different PR is already was already in the drafting phase via #824 which will reuse existing methods in the library (instead of making raw HTTP calls from scratch), + add more solidified deprecation messaging