Forman 130 lazy load dataset details

[forman]

After merging this PR, xcube serve will behave differently:

• The response of datasets?details=1 will now contain dataset descriptors, whose placeGroups GeoJSON feature collections will no longer have a features field.
• Clients must therefore call datasets/{dataset}/places/{placeGroupId} to explicitly receive a place group including all GeoJSON features.

WARNING: Deploying new server instances will require to also deploy updated xcube-viewer instances. See xcube-dev/xcube-viewer#65 and xcube-dev/xcube-viewer#61

Closes #130.

[codecov-io]

Codecov Report

Merging #131 into master will decrease coverage by 0.17%.
The diff coverage is 68.96%.

@@            Coverage Diff             @@
##           master     #131      +/-   ##
==========================================
- Coverage   85.64%   85.47%   -0.18%     
==========================================
  Files          71       71              
  Lines        6620     6665      +45     
==========================================
+ Hits         5670     5697      +27     
- Misses        950      968      +18

Impacted Files	Coverage Δ
xcube/webapi/app.py	100% <ø> (ø)	⬆️
xcube/webapi/controllers/places.py	95.45% <100%> (+0.53%)	⬆️
xcube/webapi/controllers/catalogue.py	80.45% <29.16%> (-10.63%)	⬇️
xcube/webapi/handlers.py	90.46% <64.7%> (-1.72%)	⬇️
xcube/webapi/context.py	80.41% <78.68%> (+1.4%)	⬆️

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[AliceBalfanz]

Should these changes be included into the CHANGES.md? Because there is an addition in the possibilities of regesting places?

[forman]

Should these changes be included into the CHANGES.md?

Yes. It is an improvement.

Because there is an addition in the possibilities of regesting places?

I don't understand this.

[AliceBalfanz]

Because there is an addition in the possibilities of regesting places?

I don't understand this.

Sorry, very bad English... What I meant to write: Shouldn't the changes be included in the CHANGES.md because amongst others there is a change of how places are requested, and the user should be aware of this change. But you already answered, that it should be included in the changes.md :)