Move D3 to core, use non-minified vega lib to drastically speed up build time
Get non-minified js library versions

There are two benefits of this:

1. The uglify task runs faster on non-minified inputs
2. We'll get meaningful source maps for our library code as well,
   which may be helpful for debugging JS in the future.
Changing from clang to gcc to fix build issues.
Merge pull request #191 from girder/vega-client-plugin

Move D3 to core, use non-minified vega lib to drastically speed up build...