Replaced imports by LodelContext.expose_modules() calls
Theorically all of those imports were tested by unit testing, but we've got no inssurance about that.
And even if unit tests had check for syntax errors, all pieces of code were not tested. We cannot
be sure that an import was missed or forgotten...
The automatic UID creation by datasource implementation implies somes changes :
The UniqID datahandler has to call the datasource
LeObject has to be able to determine wich parent class define its UID datahandler
[NOT IMPLEMENTED] the datasource should be able to select with an abstract LeObject as target ( see #92 )