Add docs and playground link

[khushal87]

This PR introduces the following features:

• Add links to react-native-elements docs (https://reactnativeelements.com/).
• Add links to the Playground (https://react-native-elements.js.org/). (The above two will increase user engagement with the app, a playground, as well as help users, refer docs instantly whenever they need)
• Improved code structure
• Fixed icons
• Subheader missing text

Note: Some of the links are non-uniform as they have a different name in docs and have a different name in the playground which makes it difficult to manage the URL forwarding. Eg: For a Bottom sheet component, the docs URL is https://reactnativeelements.com/docs/bottomsheet and the playground URL is https://react-native-elements.js.org/#/bottom-sheet. An extra "-" makes it non-uniform. The fix could be making the URLs uniform in both docs and the playground or add different names for different views in the demo app. Therefore I need suggestions on it @flyingcircle. Kindly review the PR and give your suggestions on the topic. Which approach should I go for and in that case should I make the URL uniform in both the applications(demo/playground)? Thank you @flyingcircle.

I completely understand that in the future we would be moving to only one platform and the playground and docusaurus website would be the same. At that time, I will update the views here.

Reference issue - #195

[khushal87]

@flyingcircle kindly review

[khushal87]

@pranshuchittora @flyingcircle please review.