prevent loading tokenizer on import (#1432)

also adds sentencepiece dep for exe
moved vicuna imports to after an if statement
in general we should avoid importing files that load whole models as
global variables

requirements.txt

@@ -28,6 +28,7 @@ scikit-image
 pytorch_lightning # for runwayml models
 tk
 pywebview
+sentencepiece
 
 # Keep PyInstaller at the end. Sometimes Windows Defender flags it but most folks can continue even if it errors
 pefile