Re-use the existing message about partition type and size,
since I don't want to introduce another message with all the
specifics; give a works-always message instead.
The check itself is also straightforward, avoiding all of the
nuances and technically-this-might-work cases: FAT32, 300MiB+.
FIXES#607
Modules nearly always have a Config and either a Job or ViewStep
as their "top level" components. Everything else is implementation-
detail. The *partition* module was unusual in that those two
"top level" components were tucked away in subdirectories.
Shuffle them to the top: this makes it more clear that these
two files are there to coordinate the module.
