addMarkerBySchoolYear() method implemented

Add markers according to available Grad Rate data

Signed-off-by: Stanley Lai <stanleylai.sg@gmail.com>
ControlP5 UI with working filters by School Year

ControlP5 radio buttons will now filter results, and show markers of schools that have data for that school year.

Signed-off-by: Stanley Lai <stanleylai.sg@gmail.com>