Abstract tableName() by adding new function isQuotedIdentifier() to databases.

Abstract tableName() by adding new function isQuotedIdentifier() to databases.
This fixes bug in DatabaseOracle.php tableName() on line 671 and allows it to call
the parent implementation instead of copying it with different quotes.
Adapt Mssql addIdentifierQuotes(). Replace its addIdentifierQuotes calls with addQuotes
as it's what it really is. The serialize() is probably unneeded, since I don't think it will
ever be called with objects but I kept it anyway.