Rating and Subject fixes

- Added sorting so that Subject view will show units from highest rating
to lowest
- Subject view now shows rating percentage and number of votes
- Up/Down rating is now button to call set_rate_up/down function through
POST, unit id for function call obtained through hidden field
- unit_m now includes rate_status data before sending back to main
(previously a separate function call from controller, now $unit that is
passed from controller to view contains rate_status data)
Rating fix #2

- removed subjects controller sort function
- modified subjects model to sort units by rating
- added drop table to schema sql
- removed data from schema sql for individual tables
- added complete database as skilljoy.sql which contains structure +
data, including drop table statements
Restored subject controller and model changes

Reverted back to using a sorting function
Merge pull request #8 from m-mmoocs/Rating-and-Subjects-Fixes

Rating and Subject fixes
before merge