EESchema. Refactor label name feature, add/update all hierarchical labels at once, allow sheet pins top & bottom

1. Similar to NetBeans "Refactor". That is, rename a label
   (OLD_LABEL_NAME) once --> _LABEL_NAME
Changes *all* labels 'OLD_LABEL_NAME' to 'NEW_LABEL_NAME'
This would apply to all label types.

2. Import Sheet Pins (EESchema). Make similar to PcbNew, 'Import Net List'.
Import *all* hierarchical labels in *one operation*.
Add "distribute evenly" option to arrange each pin with even spacing around all 4 sides.
Add "in alphabetical order" feature to further organise label placement.

3. Allow placement of pins at all 4 sides of a hierarchical sheet (not just left and right sides).