Add new search and remove commands

search: new command to search packages across repos

A wrapper around aptly repo search with extra features:

• filtering by --repo
• filtering by --distro
• useful output --format options:
  • full: like aptly
  • short: one package entry for all archs
  • version: versions summary
  • arch: archs summary
  • count: package counts

remove: new command to remove packages from repos

A wrapper around aptly repo remove with extra features:

• same options as arepo search which can be used to refine queries
  • filtering by --repo
  • filtering by --distro
  • useful output --format options
• unlike search, remove package query must be explicit (default Name would remove ALL packages)
• --ask safety option (default) prints affected packages in specified --format and asks for user confirmation before package removal