Correct model and migration

Update to the new risk assessment model, include the corresponding
migration script.
Remove references to removed RA objects from UI

Removing Threat, Vulnerability and Template
Adding RiskAssessment model
Fix "+ Create New" link for RiskAssessments in LHN
Alphabetized services to be easier to find
Basic modal for Risk Assessment.
Adding python model package init.
Broken, saving current work

Program is jammed between a mapping and an actual relationship. Need to
clarify this with Dan/Brad.
Modal should work properly when relationship with Program is corrected.
Mixed risk_assessments into Program
Progress on tier2 mustache for risk_assessments
Get people related to risk_assessment to show properly
Change widget name to Risk Assessments.
Description and notes now properly bound to form fields.
Edit link now works correctly on Risk Assessments.
Cleanup remnant of risk_assessments template view.
Merge branch 'develop' of https://github.com/reciprocity/ggrc-core into feature/risk_assessment
RBAC for RiskAssessments complete.
Added file attachments to risk assessments.
Removed some references to task and added comments to follow up on correct authorization for file uploads on risk assessments.
Allow ProgramReader to read Documents.