Use lodash._isEqual for checking eeObject equality

[kylebarron]

Currently we use === for checking if EE objects are identical. EE objects are a sort of JS object under the hood. This means that this is true:

const eeObject = ee.Image('CGIAR/SRTM90_V4');
eeObject === eeObject // true

but this isn't:

ee.Image('CGIAR/SRTM90_V4') === ee.Image('CGIAR/SRTM90_V4');
// false

This PR uses lodash.isEqual for checking deep equality of EE objects. This prevents unnecessarily creating new map objects when the referenced dataset is the same.