knowledge tracing and student model interaction, with a tutor.
student model builder, tests updated, docs updated
Merge branch 'master' of https://github.com/tutorgen/hpit_services into knowledge-tracing-student-model
made data storage entity dependent, updated unit tests.
Updated search hashes to be calculated from the problem start AND the current state string.
Fixed hint factory test to expect new hashing method.
added travis-test so build will pass on travis
Fixed a problem with hashing state strings.
studends tied to entities, internal plugin registering, updated ui for both, new sql database models, utils for student authorization
Merge branch 'master' of https://github.com/tutorgen/hpit_services into student-tied-to-entity
forgot to edit tests when fixing bug
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Merge pull request #46 from tutorgen/knowledge-tracing-student-model

Knowledge tracing student model
Merge pull request #43 from tutorgen/data-store-fix

made data storage entity dependent, updated unit tests.
Merge branch 'master' into student-tied-to-entity
Merge pull request #44 from tutorgen/student-tied-to-entity

Student tied to entity
Merged master into problem_generator. Fixed conflicts.