changed slow list[0] to fast next(generator)
optimization: from three lists to one; removed self.snap_list_unordered and self.snap_list_ordered; use self.snap_list instead
ignore hidden oa_objs when collecting them for the add-operator
print errors to blender info area instead of the OAError-labels
inserted some If DEBUG before print-statements
removed OAErrors
removed legacy code (un/register apply_oa_id) and error checking_multiple_tags because collect_models is already checking for that
removed lagacy code: error_checking_multiple_oa_group -> because it is allowed since a lot of commits back
minor rename
collect_models-errror-checking: check for simp and impl in same group
collect_models-error-checking: check for multiple snap point objects in same group
new function: get_editor_tags
collect_models-error-checking: check for tag values and keys more sophisticated