A bugfix in SLU preprocessing

Replacements must be whole words only ("Plzeň" got changed to "Plzň"
because of the "ze" -> "z" normalization rule).

Works well with bootstrap, hope I didn't do anything wrong.
Fixes to SLU for cities

Just using larger previous context helps for "from STOP=X in CITY=Y"
(e.g. "ze zastávky janáčkovo dívadlo v brně").

Cannot use commas in bootstrap transcriptions (they are not split in
tokenization and will spoil the previous word).