Move sequencer, connector, and MIME type detector projects into an "extensions" folder (under trunk)

DNA 0.1 introduced the concept of a sequencer, and we created a "sequencers" folder (under trunk) where we've been putting the projects that provide sequencer implementations. With DNA 0.2, we've also introduced the concept of a connector and - not surprisingly - placed all of the connector implementations in projects under a "connectors" folder (under trunk). Recently we introduced a third kind of extension point: the MIME type detector. We currently have only one implementation, but there certainly is the possibility that we'll have more. And really, the "dna-maven-classloader" is another type of extension.

But three different types of "extensions" doth make a pattern, and I wouldn't be surprised if we have more. Rather than have different folders under trunk for these different types of extensions, I'd like to make a single "extensions" folder (under trunk) and move all sequencer, connector, MIME type detector, and Maven class loader projects into that one folder. The project naming convention helps keep things clearly identified, all of these extensions really are optional (easier to describe in the documentation), we'll simplify the directory organization, and it will make it easier if any extension project wants to provide more than one type of extension (say, a detector AND a sequencer).

Pinging the dna-dev@ list to see when might be a good time to schedule this.