API: Migrate gas median

[ethedev]

Migration of the gas median endpoints from the data api to the api.

3 endpoints to migrate from here:

app.get('/median', mongoFunctions.getLatestMedian);
app.get('/median-history', mongoFunctions.getMedians);
app.get('/median-range', mongoFunctions.getMedianRange);

[ghost]

https://github.com/UMAprotocol/UMIPs/blob/master/UMIPs/umip-129.md

Let's use this python script instead of the big query. I can do that as well.

[ethedev]

@byterose best it be done in golang and if you understand it well you can just convert it from python!

[ghost]

@byterose best it be done in golang and if you understand it well you can just convert it from python!

That's what I meant, yes ^^