feat(Header): Add background image

[MHase]

Issue: #1551
Added possibility to pass backgroundImage prop which is simply source prop like in Image component :) e.g. :

source={{ uri: 'http://google.com' }}

[codecov]

Codecov Report

Merging #1556 into next will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##             next    #1556   +/-   ##
=======================================
  Coverage   76.23%   76.23%           
=======================================
  Files          32       32           
  Lines         606      606           
  Branches       78       78           
=======================================
  Hits          462      462           
  Misses        125      125           
  Partials       19       19

Impacted Files	Coverage Δ
src/header/Header.js	100% <100%> (ø)	⬆️

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[iRoachie]

Brooooo this PR is 🔥

[iRoachie]

There is one thing we way want to add. The ImageBackground component has a imageStyle prop which is used to style the Image https://facebook.github.io/react-native/docs/imagebackground#imagestyle.

So the user can access this, we may want to add backgroundImageStyle prop.

OR we could say that it has all the props from the ImageBackground Component and we'd need to update the typescript definitions to say that.

[iRoachie]

Man this looks so amazing 💯