1093 [image_picker] Fixed a crash that would occur when called in quick succession on Android (cla: yes)

1102 cleanup (cla: yes)

1103 Migrate independent plugins to AndroidX (cla: yes)

1104 Include Android SDK 27 in the docker image and accept licenses (cla: yes)

1105 update change log for url launcher (cla: yes)

1106 [firebase_ml_vision] Set minimum iOS to 8 (cla: yes)

1108 Remove ‘init’ static method (cla: yes)

1109 Update all plugins to minimum iOS 8.0 (cla: yes)

1112 [IAP] Update README (cla: yes)

1115 Migrate remaining plugins to AndroidX (cla: yes)