Add uppercase prop to Text, make button text uppercase by default on Android

[kherock]

This reimplements the behavior available in previous versions of NB. I chose uppercase over capitalize since it better corresponds to the text-transform CSS property value.

To force lowercase text in buttons on Android, the component is used like

<Button>
  <Text uppercase={false}>Tap here</Text>
</Button>

This also includes some updated TypeScript definitions.

[kherock]

@shivrajkumar I noticed in your commit that merges this is inconsistent about using uppercase or capitalize in the propTypes vs what is used in the actual component. The Text type definition is also missing the new property. I'll just rebase this PR.

Btw, I really think it should be uppercase instead of capitalize (though I accidentally said the wrong thing in my commit message). Capitalize Only Affects First Letters while UPPERCASE LOOKS LIKE THIS

Plus, the actual underlying call is String.prototype.toUpperCase()

[kherock]

Ok I rebased and adjusted the commit to only include the relevant stuff. I realized that there was still the capitalize prop that must have been copied/pasted from the 1.x component and cleaned that up. Can you make sure you include the updated type definitions? I need those :P

[kherock]

@shivrajkumar sorry to ping you again, but could I at least have some acknowledgement of when this can get integrated? Or what problems you might have with my additions?

[SupriyaKalghatgi]

Merged with 2.1.4