Replace all remaining json_decode s

* Replaced all remaining json_decode's that were added in the meantime
11 jobs for 57-implement-system-to-show-api-warnings in 2 minutes and 37 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Lint
passed #7101
lint:lint-php5.4

00:00:48

passed #7102
lint:lint-php5.6

00:00:48

passed #7103
lint:lint-php7.0

00:00:36

passed #7104
lint:lint-php7.1

00:00:48

passed #7105
lint:lint-php7.2

00:00:21

 
  Codesniffer
passed #7106
allowed to fail
codesniffer

00:00:51

 
  Unit
passed #7107
unit:testBasic

00:00:55

passed #7110
unit:testPageProperty

00:00:55

passed #7108
unit:testRead

00:00:53

passed #7109
unit:testReadAssertFail

00:00:41

passed #7111
unit:testUserProperty

00:00:53