Remove gradebook schema

[jrm86]

The schema named Gradebook has been removed. All gradebook schema qualifiers have been removed. Privileges on the current schema are revoked from public and granted to current_schema

Closes #74

[afig]

Thanks for opening the PR @jrm86. I have successfully installed Gradebook with these changes in place.

One thing to consider is that for installation, simply setting the search path with a command such as SET search_path TO 'gradebook' is sufficient. However, that setting only applies for the current session. This means that it does not apply for any subsequent sessions, including ones opened by some import procedures.

Since the import procedures for course schedules and rosters are non-interactive, the previously mentioned command cannot be run. Instead, the default search_path for the user that the import procedure will be run as needs to be changed to the appropriate schemas. This can be done with a command like:

 ALTER ROLE role IN DATABASE database SET search_path TO schema1, schema2, pg_temp;

In the above command:

• role and database should be changed to the appropriate role and database, respectively
• The IN DATABASE database portion is optional. Leaving it out sets the default search_path for the provided role universally (in all databases)
• Any number of schemas can be provided in place of schema1, schema2, however pg_temp should always be the last schema listed for security reasons

[jrm86]

Thanks for the detailed feedback and recommendation, @afig. I've made changes to the import READMEs to address that concern.