[FLINK-1318] CsvInputFormat: Made quoted string parsing optional with configurable quote character. Simplified parsing

- Parsing of quoted strings is disabled by default
- When enabling a quoting character needs to be specified
- If quoting parsing is enabled, Strings are parsed as quoted if the first character is the quoting character (leading and tailing whitespace characters are NOT ignored)
- If quoting parsing is enabled and the first character is NOT the quoting character, Strings are treated as unquoted
- Quoted parsing fails 1) if the last character of the field ist NOT the quote character (tailing characters), or 2) the closing quote character is missing

This mode of operation differs from the previous implementation:
- Leading and tailing characters were ignored in case of quoted strings but would have caused problems if whitespaces were used as field delimiters.
- double quote characters could be used to escape quotes in quoted strings

This pull request builds on PR #264 (only the last commit is valid)