Implementation  of Import/Export a Sequence and rspec

 - Include a type property in export json to distinguish activity and
 sequence.

 - Add spec for importing functionality.

 - Using ajax for importing activity/sequence

 - Do not redirect when import fails instead show error in the
import popup.

 - Maintain record for importing activities/sequences. Store the details of user,activity,sequence, export_site and
time of import while importing  a sequence/activity so that it can be
backtraces when required.