Add missing django properties for indicator.

Weighted service frequency for low-income population was missing some properties definitions, causing it to not save/display properly.
Fix division by zero for weighted service frequency.

If no population found within boundary, result returned was NaN.
Add missing Angular translation for low-income service frequency
Merge pull request #325 from flibbertigibbet/feature/fix-frequency-weighted-low

Feature/fix frequency weighted low