Trim unneeded Moose::Autobox use from the App::Cmd layer

Moose::Autobox  pulls in 27 extra dependencies that are not really used within the command ecosystem.

None of dzils' own commands use it, and only `Dist::Zilla::App` has any use of it which is a mere `->flatten` call.

Thus, these reasonably simple changes remove those 27 dependencies:

```
git checkout trim_autobox_command
PERL5LIB="$PWD/lib" strace -e trace=open -o /tmp/trace perl -S dzil version ; wc -l /tmp/trace 
dzil (Dist::Zilla::App) version dev (/home/kent/perl5/perlbrew/perls/blead/bin/dzil)
296 /tmp/trace
PERL5LIB="$PWD/lib" /usr/bin/time -v bash -c 'for i in $(seq 0 20); do perl -S dzil version; done' |& tee /tmp/fast
```
```
git checkout trim_autobox_command~3
PERL5LIB="$PWD/lib" strace -e trace=open -o /tmp/trace perl -S dzil version ; wc -l /tmp/trace 
dzil (Dist::Zilla::App) version dev (/home/kent/perl5/perlbrew/perls/blead/bin/dzil)
323 /tmp/trace
PERL5LIB="$PWD/lib" /usr/bin/time -v bash -c 'for i in $(seq 0 20); do perl -S dzil version; done' |& tee /tmp/slow
```

```diff
--- /tmp/slow   2014-10-31 06:57:43.784203263 +1300
+++ /tmp/fast   2014-10-31 06:57:27.225209917 +1300
@@ -20,20 +20,20 @@
 dzil (Dist::Zilla::App) version dev (/home/kent/perl5/perlbrew/perls/blead/bin/dzil)
 dzil (Dist::Zilla::App) version dev (/home/kent/perl5/perlbrew/perls/blead/bin/dzil)
        Command being timed: "bash -c for i in $(seq 0 20); do perl -S dzil version; done"
-       User time (seconds): 8.98
-       System time (seconds): 0.95
+       User time (seconds): 7.91
+       System time (seconds): 0.85
        Percent of CPU this job got: 99%
-       Elapsed (wall clock) time (h:mm:ss or m:ss): 0:09.94
+       Elapsed (wall clock) time (h:mm:ss or m:ss): 0:08.77
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
-       Maximum resident set size (kbytes): 144352
+       Maximum resident set size (kbytes): 136400
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
-       Minor (reclaiming a frame) page faults: 160298
-       Voluntary context switches: 48
-       Involuntary context switches: 55
+       Minor (reclaiming a frame) page faults: 150185
+       Voluntary context switches: 47
+       Involuntary context switches: 51
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
```

Note you need either a clean install with only dzil's `::command`'s or to have only `::command`'s without `Moose::Autobox` to experience this benefit, but that's very easy to achieve.