Code cleanup and manifest thinning

[dschach]

Remove unnecessary static resources Visualforce pages now use standard controller and an extension to enforce security Add some setCurrentPage in Apex tests to make extension testing more smooth Add a flexipage for Survey Taken (to demonstrate that feature) Move all styling to standard SLDS and update BEM notation Delete custom SLDS static resource Clean up test code and some assertions Remove unused methods only covered in test classes but not used Change pageMessage UI to SLDS toast Update scratch org definition to enable Sites (but not create one - do that manually) Curly brackets around single-line if/else outcomes to avoid possible future problems

[dschach]

Please add to the readme that after updating to this, the ONLY surveyforce static resources needed are the SurveyForce folder and the UserGuide pdf.