* moved repository url to changeable environment variable

* move stable diffusion repo itself to env

* added missing env

* Remove default URL
Co-authored-by: AUTOMATIC1111 <16777216c@gmail.com>

Default value is the first value of selectables.
Particually, None in styles.

made save style button not die when you cancel

Tag/Option Parsing in Prompts From File

add --ckpt-cache option for faster model switching

- Check the actually used `$python_cmd` and `$GIT` executables instead
  of the hardcoded ones
- Fix typo in comment

This is only necessary when you have to train,
and compiling model produces warning.