visualize dependencies as a tree

[vn971]

When installing or upgrading packages, visualize the the expected changes / depedency hierarchy with a tree:

gam  (AUR)
├── python-dateutil
├── python-google-api-python-client
├── python-google-auth-httplib2
├── python-google-auth-oauthlib  (AUR)
│   └── python-requests-oauthlib
├── python-google-auth
├── python-httplib2
├── python-mock
├── python-passlib
└── python-pytest

As a first implementation, just printing AUR deps could work. This can be further improved by printing pacman deps, showing broken AUR/pacman deps right in the tree, and maybe visually separate AUR and "repo" packages with color.