Rc -> master 2.15.3

* All modules that use `streamhub-sdk/storage` will now store content with a key parameterized by both content id and collection, instead of just content. This fixes a bug that would cause content to render/update badly if e.g. the same tweet was in two different Collections (LF-14001);
* Upgrade to [streamhub-share 0.1.5](https://github.com/Livefyre/streamhub-share/pull/7), which fixes a bug where the share dropdown on ContentViews would be a less-than-ideal width in Safari and Firefox.