Bugfix: External apps by shares

Opening shares in "Shared with me" section was broken. We have added property `mimeType` by the build of a shared resource, so that the external apps can be found for it. 

We fixed passing the fileId property for the context actions.

https://github.com/owncloud/web/pull/5907
https://github.com/owncloud/web/issues/5906
