Added string formatting for molecular weights in HTML output.
Added string formatting for molecular weights in HTML output.

We don't need ten decimal places for molecular weights, especially since
most of them are not significant. This commit uses two decimal places for
everything. I also added units so that it's clear what units the molecular
weights are in.

enochd/RMG-Py,pierrelb/RMG-Py,nickvandewiele/RMG-Py,faribas/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,nyee/RMG-Py,chatelak/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,faribas/RMG-Py,comocheng/RMG-Py,pierrelb/RMG-Py,KEHANG/RMG-Py,nyee/RMG-Py,KEHANG/RMG-Py