Template play vars after reading them

Fixes #9242
Revert "atfork import warning should be suppressed when system_warnings = False"

This reverts commit a175168686abedaad88051aedc2dab3d164ba792.
WIP on data structure processing patterns.
Add submodule references since v2 development will need them, the tree obviously does
not need two copies.
Work in progress on task loading.
Attribute defaults and optional accessors.
Attempt to clean up the munging functions a little.
add a proxmox inventory plugin
add host variables (proxmox_vmid, proxmox_uptime, proxmox_maxmem, ...)
add _meta in the list json
add --pretty for debuging purpose