trace-summary fails with `ImportError: No module named SubnetTree` and

[Jay R. Wren]

Deps are missing from the trace-summary package.

expected: the trace-summary command to work.

what happened:

```
$ trace-summary
Traceback (most recent call last):
  File "/usr/bin/trace-summary", line 19, in <module>
    import SubnetTree
ImportError: No module named SubnetTree
```

After resolving the dependency myself, by installing the python-subtree package with `apt install python-subnettree`, the command still does not work:

```
$ trace-summary
Can't read pcap trace: 'ipsumdump' is required.
```

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: trace-summary 0.84-1
ProcVersionSignature: Ubuntu 4.15.0-42.45-generic 4.15.18
Uname: Linux 4.15.0-42-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
Date: Fri Jan 18 15:55:30 2019
PackageArchitecture: all
ProcEnviron:
 TERM=tmux-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: trace-summary
UpgradeStatus: Upgraded to bionic on 2018-06-27 (204 days ago)