reload stores of tabpanel children on 'activate' event

reload stores of tabpanel children on 'activate' event

Tabpanel reload -> send 'show' event -> reload child panel store

do not work with ExtJS6

but

Tabpanel reload -> reload  child panel ->  child send 'show' event ->
reload a grid store in the panel still works

so we don't blindly replace the 'show' events everywhere but only
when the event was expected by a direct child of a tabpanel