Re-add line-height in unpadded sortables

Summary:
line-height: 0 makes unpadded sortables with text look
ugly:
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The line-height: 0 was to make sure the image wasn't positioned above a non-existant text baseline, unnecessarily making the sortable card larger. Instead, this diff uses `vertical-align: bottom;` on images to have the same effect on image sizing without making text appear on top of itself.

Test Plan:
Loaded this item:
http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22**Which%20shape%20are%20the%20clues%20describing%3F**%5Cn%5Cn%5B%5B%E2%98%83%20matcher%201%5D%5D%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F1379734e507821433c3bda2f1177fda47da3f10e.png%22%3A%7B%22width%22%3A400%2C%22height%22%3A266%7D%7D%2C%22widgets%22%3A%7B%22matcher%201%22%3A%7B%22type%22%3A%22matcher%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22left%22%3A%5B%22**is%20not%20round**%2C%20so%20it%20is%20not%3A%20%20If%20I%20add%20some%20more%20words%2C%20it%20gets%20yucky!!%22%2C%22**is%20a%20quadrilateral**%2C%20so%20it%20is%20not%3A%22%2C%22**has%20%244%24%20right%20angles**%2C%20so%20it%20is%20not%3A%22%2C%22**has%20%244%24%20sides%20of%20equal%20length**%2C%20so%20it%20is%20not%3A%22%2C%22must%20be%3A%22%5D%2C%22right%22%3A%5B%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F9bf34a29bc62816f07057d9e571de844df484cd9.png)%22%2C%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F199a93b886364a922bb38008d9c0a08221ca4dac.png)%22%2C%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F5b842c6adbdf4de4dba70296479b1954a2362785.png)%22%2C%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F4a8715a6c6537a0708df913e628906bc0494fd05.png)%22%2C%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fd7e87a3d879924b2a1dbf230d26c2ff999761993.png)%22%5D%2C%22labels%22%3A%5B%22**The%20shape%3A**%22%2C%22%24%24%22%5D%2C%22orderMatters%22%3Afalse%2C%22padding%22%3Afalse%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22Arrange%20the%20cards%20in%20the%20correct%20order.%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22hints%22%3A%5B%7B%22content%22%3A%22The%20shape%20is%20not%20round%2C%20so%20it%20cannot%20be%20a%3A%20%20%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F9bf34a29bc62816f07057d9e571de844df484cd9.png)%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F9bf34a29bc62816f07057d9e571de844df484cd9.png%22%3A%7B%22width%22%3A100%2C%22height%22%3A100%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22The%20shape%20is%20a%20quadrilateral%2C%20so%20it%20cannot%20be%20a%3A%20%20%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F199a93b886364a922bb38008d9c0a08221ca4dac.png)%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F199a93b886364a922bb38008d9c0a08221ca4dac.png%22%3A%7B%22width%22%3A100%2C%22height%22%3A100%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22The%20shape%20has%20%244%24%20right%20angles%2C%20so%20it%20cannot%20be%20a%3A%20%20%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F5b842c6adbdf4de4dba70296479b1954a2362785.png)%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F5b842c6adbdf4de4dba70296479b1954a2362785.png%22%3A%7B%22width%22%3A100%2C%22height%22%3A100%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22The%20shape%20has%20%244%24%20sides%20of%20equal%20length%2C%20so%20it%20cannot%20be%20a%3A%20%20%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F4a8715a6c6537a0708df913e628906bc0494fd05.png)%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F4a8715a6c6537a0708df913e628906bc0494fd05.png%22%3A%7B%22width%22%3A100%2C%22height%22%3A100%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%5D%7D
locally, and made sure that images didn't have much padding and were centered in their sortable cards
 * also added random text to the sortable cards and made sure they still looked good.

Reviewers: alex

Reviewed By: alex

Differential Revision: http://phabricator.khanacademy.org/D10979