make range select work in a more intutive fashion

in zabbix, checkbox range can be selected by holding down ctrl, clicking in a checkbox, then clicking in a second checkbox while holding down ctrl again.
this is different from any other applications, and a bit cumbersome - one has to know that range selection will be next, which is not the case often enough.

instead or additionally, a mode like in other applications should be supported - holding down shift and clicking in a checkbox should operate on a range since the previously operated checkbox.

this would allow users to discover this feature without knowing about specific implementation details in zabbix.