project.zip does not preserve symbolic links - might want to add project.tar

**Tool:**
http://172.26.0.2/cb (local DevEnv)

**Bug Description:**
When the project.zip archive is uncompressed, there are no symbolic links. This means two things: 1. It isn't possible to tell which of the conformers is the default. 2. One of the conformer directories is duplicated entirely, which wastes space.

When I look at the directory structure on the back-end, it occurs to me that we probably need to retool how we do our symbolic links. See Additional context.

**To Reproduce:**
Build any multi-conformer glycan using any of the oligosaccharide modeling front end. Choose to build at least one of the available conformers. On the downloads page, click "Download All Structures". Unzip the file. Try to figure out which conformer is the default.

**Expected behavior**
I expect the top-level 'default' object to be a symbolic link to one of the other directories.

See also Additional context, below.

**Additional context**
Adding symbolic links might cause trouble for some users if their filesystem doesn't support symbolic links. Most *NIX systems should be fine. It will be worthwhile to test on Windows and Mac.

We will need to employ some fancy compression for returning files to users. In the set below, 'default' points to something outside its directory level. The others do, too. The user will need the non-default directories to contain actual data, but the 'default' directory should symlink to one of the other directories at that level. Many apologies for the annoyance you will probably feel trying to correct this.

├── Requested_Builds
│   ├── 5ogg_6ogg -> ../Existing_Builds/5ogg_6ogg
│   ├── 5ogg_6ogt -> ../Existing_Builds/5ogg_6ogt
│   ├── 5ogt_6ogg -> ../Existing_Builds/5ogt_6ogg
│   ├── 5ogt_6ogt -> ../Existing_Builds/5ogt_6ogt
│   └── default -> ../Existing_Builds/default