started adding video sharing support

Actually, it is just creating a SnapReceivedEvent with the uri. But it remains to translate the content:// string to a file:// string.
Convert content URI to file URI for videos
fixed minSdkVersion

which I lowered before, for some reason...
Completed video sharing support

Prevent Snapchat from deleting videos shared with Snapshare. Reset snapshare marker variables where necessary so that videos can be deleted when normally recorded inside Snapchat.
Documentation improved.
Corrected .gitignore to ignore all build/ dirs.
Merge branch 'video-sharing'

Successfully added video sharing support.