Elevation and Shadow support

[JakeWoki]

Per the material design spec this component should have a default elevation of 8dp and cast a shadow upwards on to the content above it - it doesn't seem to do that currently regardless of elevation being set in the layout or in code.

[armcha]

#13

[JakeWoki]

@armcha

Where?

[mecoFarid]

@JakeWoki, Shadow pull-request added here. If not accepted, you can use still manually implement the library in my fork.