Add Image_question to the activty_runtime_api
blob.rb: Add mimetype,  file_extension, checksum

Learner.rb: Add assocation to lightweight_blobs <=> blobs
Also: add methods to pull content from URL, generate checksum
&related tests.
ProcessExternalActivityDataJob -- adding image question answers.

proceess_external_activity_data_job.rb: support  image_question
&update spec / features
blob.rc typo: leightweight_learner ➙ lightweight_learner
move webmock/rspec require to spec_helper.
maven_jnlp_server_spec.rb : Mock web request to jnlp server
activity_runtime_api_spec.rb :  Fix broken test, external_id is a string
00_core_extensions.rb: Ensure that Object#display_name works for Objects

Used to only work for ActiveModel classes.
Fix typo in spec.
blob_spec.rb : Fix typo in text of assertion.
Merge pull request #39 from concord-consortium/np_add_lightweight_image_question_answer

Add lightweight image_question 's to ExternalActivty templates

include lightweight image_question answers in reports