The portable version will prefer to create it's settings in it's own
directory and only fallback to a user-specific path
($LOCAL_APPDATA/openslides) if this directory is not writable
- Make notice that prebuild openslides.exe is used instead of
compiling it from source a bit friendlier so it isn't confused
with an error
- Reduce span of try/except to avoid masking errors when we only
want to gracefully handle the case that no compiler is present
- Show "success" message after creating the portable zip
