Decrease splinter timeout to 3 seconds

@alexmuller
@maxfliri
Allow user access to upload based on permissions

@alexmuller
@maxfliri
Refactor tests for readability

@maxfliri, @alexmuller
Permissions checking extracted to class

@alexmuller, @maxfliri
Add unit tests for Permissions class

@maxfliri, @alexmuller
Method renamed to a more sensible name

@alexmuller, @maxfliri