New subcommands for pkgdev #79

This is a start of a plan, something like a pre-RFC.
I think we should add new functionality to pkgdev, which we "steal" from other dev-scripts. But this could result in a mess, so I want to pre-plan, list the desired sub-commands, so we have a clean path.
Also it would be better to select other first letter, so auto completion is faster.

• keyword: perform the things ekeyword does. Maybe improve with bug number handling (use nattka)
• file-bug {stablereq,keywordreq}: file those bugs, fill the fields, maintainers, populate the dependencies list. Maybe will use nattka (adding an optional dependency).
• scan (?) - just alias for pkgdev scan
• cleanup - do various cleanups by "queries" over packages (maintainers, days, stable/unstable only). Maybe it should be interactive? Do think how we can cleanup FILESDIR