MixCloud oEmbed support

Adding support for MixCloud oEmbed
Added MixCloud oEmbed to oembed_providers_list
Merge branch 'develop' of https://github.com/diaspora/diaspora into develop
oembed_providers.yml added for custom (outside of ruby-oembed) oEmbed providers.
Merge pull request #4131 from Ruxton/patch-1

Refactoring oEmbed Providers & Adding MixCloud oEmbed support
Fix preview with locator feature
Merge pull request #4147 from svbergerem/post-preview-locator

Fix preview with locator feature
try to fix Jasmine failure on CI by not overwriting app.views.Location in spec
bump recommended ruby version to 1.9.3-p429