We reverted to using the checkout instead of an installed openslides
version when building the portable, but we still want openlides to be
placed together with all the other packages
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
