Remove all remaining GParamSpec name and blurb strings (and fix
indentation while we're there), and add G_PARAM_STATIC_STRINGS to all
paramspecs that were lacking it.
Since we can't align buttons to half-character positions, they end up
looking more random than centered:
| <Add> |
| <Edit...> |
| <Delete> |
So just let them be left-aligned instead. It looks better.