Added SlideShare support

- added view for slideshare for embedding
- added content validation to retrieve slideshare id
- fixed issue with schema files that still had Github conflict markers
Fixed server 404 error

- fixed to handle 404 error if slideshare with invalid link was sent to
retrieve the id
Fixed Slideshare issues

- fixed issue of page trying to add subject relation when no subject was
selected
- fixed a line accidentally deleted when fixing 404 error
- fixed subject issue
Merge pull request #10 from m-mmoocs/Slideshare

Slideshare