provide the same filter for history view as for workspace view * history_dock_widget.cc (constructor): combo-box for filter instead of line edit, new check box for enable/disable filter, connect related signals, get last state of filter and check box from settings file; (destructor): new, write state of filter and check box into settings file; (filter_activate): new slot enabling or disabling the filter; (update_filter_history): new slot for saving the filter expression when its edtitign has finished or when it was chosen from the combo box selection list (copyClipboard, pasteClipboard, selectAll): line edit is replaced by a combo box with a line edit * history_dock_widget.h: new destructor, slots filter_activate and update_filter_history, new class variables for check box, filter combo box

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