crx : chrome addons

[odnar-dev]

- create data and cache dir
- install
	- arg is addon id
	- check if addon id is valid
	- download addon metadata
	- check if addon metadata is valid
	- download addon package
	- check if downloaded package hash is valid
	- check if downloaded package is a valid crx, and convert it to a zip package
	- unpack addon zip
	- install addon 

# data available in the metadata
- status
- codebase : download url
- hash_sha256
- size
- version

# functions related to appz_install()
- crx_addon_id_valid
- crx_download_addons_metadata
- crx_check_if_metadata_valid
- crx_download_addon_package
- crx_check_addon_package_hash
- crx_check_addon_package_valid
- crx_unpack_addon_package
- crx_install_addon_package