"Insert" export and binary blobs

[RLejolivet]

While trying to export a Firebird database to MySQL by using an SQL export ("Insert"), I found the binary blobs were not exported properly. Most notably, the null-bytes don't play too well with the "string" container.

This change replaces the string escaping for all kinds of strings in the SQL export to add a few more character escapes (heavily influenced by http://dev.mysql.com/doc/refman/5.7/en/string-literals.html since MySQL is my target for those exports).

Note : a similar change may be needed for CSV export. Also, C++ isn't necessarily my most used language, code style/improvements welcome ! :)