Set default location of configuration

[codimoc]

There should be a default location of configuration for this tool under the home directory.
This location (~/.backupplan) should contain the a the plan xml defintion with a clear association between a file-name and a plab (e.g. myplan.xml for myplan) and a file with the default parameters.
These default parameter, e.g. default backup frequency, target directory and number of files to rotate, are the backbone for any other user plan.