pkg installation flow

[onur-ozkan]

The package specification have been updated. So package installation in lpm has to be updated as well. The updated specification is all about checksum validations. meta/checksums.json is renamed to meta/files.json. And the schema of the file is entirely changed as well. Sample data can be found here.

TODOs:

• Checksum related names/data-types should be updated into something related with File.
• Files(in program directory) should not be directly copied into system no longer. Instead, read the meta/files.json and do the checksum validation(for each file) before copying them into system.