Remove dependency on dateutil in memory_inspector

Remove dependency on dateutil in memory_inspector

This patch is part of an ongoing process to unbundle memory_inspector
and make it a chrome app. It removes the dependency of www_server.py
on the dateutil module, which is not part of the Python Standard
Library.

BUG=448399
Committed: https://crrev.com/2ddff339b83714e75c8da7d0be99dbc3b4c3213b
Cr-Commit-Position: refs/heads/master@{#311507}

[petrcermak, 2015-01-14 12:40:17]

petrcermak@chromium.org changed reviewers:
+ primiano@chromium.org

[petrcermak, 2015-01-14 15:47:02]

I changed the code to reuse Archive._TIME_FMT as discussed offline.

Petr

[Primiano Tucci (use gerrit), 2015-01-14 17:08:56]

LGTM. thanks

[petrcermak, 2015-01-14 17:11:58]

The CQ bit was checked by petrcermak@chromium.org

[commit-bot: I haz the power, 2015-01-14 17:13:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/850033002/20001

[commit-bot: I haz the power, 2015-01-14 18:03:09]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-14 18:03:53]

Patchset 2 (id:??) landed as
https://crrev.com/2ddff339b83714e75c8da7d0be99dbc3b4c3213b
Cr-Commit-Position: refs/heads/master@{#311507}