Show initially part of the below the fold area

In order to communicate that there is more content below.
This is related to acceptance criteria #8 of story #830.
For more details check:  https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/830

Some further improvement to consider:
- We'll need to adjust the "more details" button margin to make it fit better in the current above the fold area (0.55 em instead of the current 0.7em).
- If the panel is open, and the user clicks outside of it (e.g., over the image), the panel should close.
- We may want to eliminate the pointing-down chevron if we don't want it to conflict with the big "more details" button.

Change-Id: If14886647aa0660a524a720e8d223eca655d5f3f
Merge "Show initially part of the below the fold area"