Remove hard dependency on version 1.2.10 for log4net

The version of log4net is fixed to 1.2.10. Hence one is unable to
use the log4net extension in a project using a higher version of
log4net. I have removed this restriction.
The answer to allow for multiple versions is not to do it through Visual studio referencing at all. You lose out on a hard reference you can work against, but at least you can log with multiple versions of log4net.