Text input

[jfeng530]

Do not merge into master.

Just looking for feedback on how it looks and functions.

For this PR, we need to test the TextInput.tsx for the following things:

• [ ] Being able to adjust the placeholder text
• [ ] Being able to pass the proper onChange function and have it work properly
• [ ] Being able to adjust additional text props (i.e., secureTextEntry)

[jfeng530]

Going to merge this into master along with pavel-ilin to test authentication functionality (due to errors with Native TextInput)