Dev messages

Fix #344

Fixed by 328b7d41, 194d7e40, 7957a274, 22025e6a, 0712a6e9. Messages are now an attribute of the object (if there is messages, no attibute otherwise). The messages are added as attribute by r_wrapp. Whan an object is retrieved, in the analysis R function, the messages have been added to the output. As it can be null, if there is no messages the output will not include messages.

No need for retrocompatibility since the attribute can be null.

In r_wrapp, the returned messages can be a concatenation of new generated messages and already existing ones (a unique is applied to avoid duplicates messages). Because in some functions, some messages are generated before the test of already existing objects.

Tests are OK.