Simple customisation of indicators

[carlhiggs]

Is your feature request related to a problem? Please describe.
Currently our software calculates a core set of indicators, with a view that these could be customised. This has been partially implemented via usage of indicators.yml. However, this is over-complex and does not yet allow for readily adding new indicators using generic methods.

Describe the solution you'd like
A simple, not repetitive schema for specifying indicators to be calculated

• plain language description (language options?)
• variable name
• units (language options?)
• methods of calculation, which may be scale-dependent
• dependencies (some indicators may rely on other measures/indicators to have been calculated already)
• notes on relevance and evidence of this indicator for contributing to healthy and sustainable cities

This information could be used to calculate, store, and present graphical reporting on the indicator.