Log Message:
editors/tp-note: update to 1.21.8

Windows: default file extension is `.md`

Recent versions of `notepad` can deal with `.md` files. From this release on,
all created note files on all platforms have `.md` extension.

Configuration file: the variables `app_args.*` interpret
`{{ get_env(name="<ENVIRONMENT_VARIABLE>") }}` as templates variable.