Remove video-only restriction on playback speed feature

The playback speed controls work wonderfully on audio as well!
Fix nativeWidth() to return defaultAudioWidth

nativeWidth() was returning defaultAudioHeight instead of defaultAudioWidth on <audio> elements
Don't set .me-plugin width/height to 0

While testing 2.15.0 for upgrade in WordPress, I noticed that all video files played by a plugin were only outputting audio, no video. Reverting https://github.com/johndyer/mediaelement/commit/53810f573dd7b16693e5d5a2cfa4375e4542935e returned playback to normal. In lieu of reverting, these values can just be changed to `auto`, so that the fix for IE8 will remain.
Fix for bugs caused by #1055

Hi, 

This PR keeps PR #1055, but adds a work around for zero height containers.
When a video has width: 100%; height: 100%; on its style attribute, like on the code below the container's height would be zero.
`<video width="1920" height="1080" style="width: 100%; height:100%;">`

This PR fixes this by checking if the parent height is not zero before assigning it as the calculated height.

Thanks!
Merge pull request #1271 from rocco/patch-1

Fix nativeWidth() to return defaultAudioWidth
Merge pull request #1268 from phinze/speed-feature-for-audio-too

Remove video-only restriction on playback speed feature
Merge pull request #1273 from staylor/patch-1

Don't set .me-plugin width/height to 0
Merge pull request #1274 from maimairel/master

Fix for bugs caused by #1055
Version update
2.15.1 build
Upgraded to 2.15.1
Added new compressed files
Fixed merge issues
Fixed more merge issues