Merged beans and edef modules

The EndpointDescription class is now defined in "beans".
The "to_import" and "from_export" methods from the module "beans" are now part of the
EndpointDecription class.
Added tests for the EndpointDescription bean & I/O

The EndpointDescription is now much more usable as is, instead being just
an alternative version of the ImportEndpoint bean.

The EDEFReader now parses "array" properties as tuples instead of lists.

The ExportEndpoint bean has been updated to use the standard framework UID property
instead of the Pelix one.