schematic-view.c: Properly name GtkBuilder variables as `builder`.

`gui` is not correct, the builder just parses a XML .ui/.glade/.builder file but is not tied to the lifetime of the UI itself.
schematic-view.c, textbox-item.c: Further `gui` by `builder` replacing.
SchamticView,UI: Embed LogView into a scrolled window, make the oregano-main.ui paned vertically.
netlist-helper/editor.c,ngpsice.c: Continue replacing error dialogs by log entries where possible.