At this point the loader in lodel/plugins/multisite/run.py is theorically
complete & correct. But some features are missing in order to be able
to test & debug it ( refs #275 ).

Conflicts:
	lodel/plugins/lodelsite_datasource/fs_utils.py

Now we are able to insert a lodelsite

no debug has been made on those piece of code

As a primary_key field has to be unique, added a check at DataHandler
instanciation to make sure a field set as a pk is not set as non-unique

Modified the shortname's DH attribute value from uniq to primary_key

Switched the shortname field's DH from Varchar to Regex

No knowing what datahandler ought to be used for em_groups, I simply set
'text' in place of it. To be changed accordingly

The Plugin class and discover steps were updated. Some test are deleted
because they were obsolete (discover method do not take any argument
anymore)

Warning, may contains some bugs !!!

For the moment there is only uninstalling by name that works because #207

Clean take care of deleting plugins with same name and different versions
(the lower versions will be deleted)

Now in verbose mode we are printing all plugins, even those with duplicated
names and different versions