Fix align-content strech with multiple lines

Summary:
Fixes ```align-content:strech``` on nodes without specified cross dimension, if there are multiple lines. Currently it uses the full height of the parent, but it has to use the line height. As we don't know the number of lines until here, we need to realign the relevant children.
Closes #368

Reviewed By: gkassabli

Differential Revision: D4528559

Pulled By: emilsjolander

fbshipit-source-id: 019e6f85fa452d0c3412f711e3886f0c4452da47

Author: woehrl01