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
Fix: Loading animation doesn't disappear Android

https://github.com/johndyer/mediaelement/issues/1283
Accessibility for volume control
css class for Offscreen text.
Accessibilty slider control. Fixed controls disappearing when navigating by keyboard, so when keyboard is used to focus on video the controls will appear and not disappear until focus is is moved outside video.
update bower.json to 2.15.1
clean trailing whitespace from actionscript files
remove event listeners from flash AudioElement

should prevent double progress events firing from AudioElements that
have setSrc + load called twice.

refs #338
send `this` to dispatchEvent callbacks

as requested in #434
Update mep-feature-ads.js

view adsLayer only when the AdUrl is not empty, to have normal Play/Pause behaviour
Fix Bug to allow Fullscreen with vimeo

Theses Attributes are mentioning in the official vimeo API
http://developer.vimeo.com/player/js-api