Update Database Schema Component

Update the CDbSchema component to allow passing columns names to CDbSchema::createIndex() and CDbSchema::addForeignKey() as an array, as well as a string of comma-separated column names.
Update Framework Unit Tests

Update the frameworks unit tests to check incoming data types for the column names of CDbSchema::createIndex() and CDbSchema::addForeignKey().
Add Issue #2817 to CHANGELOG
Update Method Parameters in CDbSchema::createIndex()

Update the spelling of the third parameter of CDbSchema::createIndex() to become plural, rather than singular, to better reflect the correct data that this parameter accepts.
Merge pull request #2818 from mynameiszanders/2817-cdbschema-inconsistent-accepted-data-types-in-method-parameters

Issue #2817 - CDbSchema: Inconsistent Accepted Data Types in Method Parameters
fixed code style and phpdoc for #2817