introducing 'dump-manifest' command

[lomnido]

it can:

• create Manifest file out of given Repos (RAW mode)
• create Manifest file out of current Workspace
• also update existing Manifest file (this keeps the Groups there)
• update Deep Manifest (auto-detection)

also in regard to other changes:

• '(missing remote)' to display for Deep Manifest and Future Manifest
• allowing to ignore missing Group's items
• 'status' can speeded up by ignoring GIT remote data