Organize exception class into better hierarchy

[dai-chen]

Proposal: #179 (comment). Currently we have multiple exception classes for different error, such as:

• SqlParseException
• ParserException
• SQLFeatureNotSupportedException
• SQLFeatureDisabledException
• VerificationException
• SqlAnalysisException

It's good to have fine-grained exception but they should be organized into hierarchy with common root. In this case, we don't need to enumerate all of them to decide what HTTP error code should be returned:

    private static boolean isClientError(Exception e) {
        return e instanceof NullPointerException // NPE is hard to differentiate but more likely caused by bad query
            || e instanceof SqlParseException
            || e instanceof ParserException
            || e instanceof SQLFeatureNotSupportedException
            || e instanceof SQLFeatureDisabledException
            || e instanceof IllegalArgumentException
            || e instanceof IndexNotFoundException
            || e instanceof VerificationException
            || e instanceof SqlAnalysisException;
    }