qtutils: remove unused selected_treeitem() function

Signed-off-by: Daniel Harding <dharding@living180.net>
qtutils: remove selection_list() function

It performed the same function as the selected_items() function, so
change the one caller to use selected_items(), and remove the now-unused
selection_list() function.

Signed-off-by: Daniel Harding <dharding@living180.net>
qtutils: refactor selection utility functions

Update to avoid generating intermediate lists when direct iteration can
be used.

Signed-off-by: Daniel Harding <dharding@living180.net>
qtutils: replace selected_row() function

All uses of qtutils.selected_row() could be more cleanly written by
using qtutils.selected_item() instead, so make those changes and remove
the selected_row() function.

Signed-off-by: Daniel Harding <dharding@living180.net>
Merge pull request #380 from living180/refactor_selection_utils

Refactor selection functions in qtutils

Signed-off-by: David Aguilar <davvid@gmail.com>