Reverted back to non-threaded FileWithTimeSource.

Createing threads for each file just makes them harder to manage; every
file like this needs to spawn data on a synchronised clock, the method
which manages this will have its own thread.
Completed basic implementation of FileWithTimeSource
Changed config to XML, its easy and well specified.

Yaml does sound nice but the exact syntax is not obvious, the libraries
aren't obvious how to use and XML is just well known.
wip Started building sensor class to supoort the file IQSources.