Fix generation of ComboBox on GenericDialog.

* The current value from the property needs to be set visible.
* The signal connection needs to come after the box is populated or
it keeps changing the property value as things are added in the loop

Refs #8086
Fix defaults for boolean options property dialog in LoadDialog.

Refs #8086
Merge remote-tracking branch 'origin/bugfix/8086_alg_combobox_defaults'