PF4: Add File Upload Component

[tlabaj]

Describe the issue. What is the expected and unexpected behavior?
Introduce File Upload component according to the UI design here: https://marvelapp.com/de0ggah

This component will be introduced for uploading text files only. The user can upload a file by browsing to it, pasting its contents, or dragging and dropping it.

This is related to core issue patternfly/patternfly#2624

[mturley]

Do we have a timeline for this? I would love to do this, depending on when I can free up some time.

[mturley]

cc @mcarrano @rachael-phillips @LHinson

[tlabaj]

@mturley We are hoping to get this in for Milestone 2020.03. Code freeze is March 6th. Do you think you can pick it up?

[mturley]

Yes, I think I can start it later this week. It shouldn't take too long, judging by my PF3 implementation.

[mturley]

I expect to start on this on Monday.

[mturley]

I have an open question about the invalid state, which I detailed in the core PR here (patternfly/patternfly#2681 (comment)) for visibility from folks who were involved in that implementation.