[ENH] Allow removing a single condition in Select Rows (#1605)
[ENH] Allow removing a single condition in Select Rows (#1605)

Closes https://github.com/biolab/orange3/issues/1588

* Allow to remove the chosen condition from select rows

* minor fixes to select rows widget

* changed the sign for remove option in select rows widget

* improved the GUI for the select rows widget

* OWSelectRows: amend minor detail

cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3