CRUD of groups and assigning/revoking roles to groups and persons

finished group-role assignment tests. get_roles() no longer throws errors when no assigned roles are found (it returns an empty DataFrame instead)

removed roleAssignments as an attribute of person/group. Roles can be listed with the .get_roles() method instead

fixed update of Sample properties

Sample properties are now updated, too

fixed project attachments bug

added project tests with attachments

another sample creation test added

additional tests for pyBIS added.

version 1.4

aded experiment tests and some more tab-completitions

pybis: removed redundant text form error message - allows for more flexibility when showing the error to the user