Factorize simplejson

This patch set make it so that all imports for simplejson are done as json so if there's a need to change it to something else it will be easier.

Part of #73 (closed)

added enhancement label

It is OK, though I find this technique for importing a bit tricky. Reading any part of the code without looking at the header may lead one to think you're actually using the standard json module instead of simplejson. Using simplejson everywhere would make it clearer IMO.

Set to auto-merge.

enabled an automatic merge when the pipeline for 2163c39b succeeds

merged

mentioned in commit 0db0873f