Increase z-index to epic proportions

Closes https://github.com/waltzio/waltz/issues/254 and https://github.com/waltzio/waltz/issues/226
:boom:

Re: https://github.com/waltzio/waltz/issues/254#issuecomment-31966133
1. SASS looks awesome
2. Apparently there is no upper limit—or at least the 32 bit integer from the SO answer does not apply to Chrome.