Remove unused imports in IPython.testing
Fix test import
Added relative import of RevealExporter to __init__.py inside exporters module.
Added another missing import inside transformer module.
Merge pull request #3520 from damianavila/import_reveal

Added relative import of RevealExporter to __init__.py inside exporters module
Merge pull request #3514 from minrk/ui-state-disabled

use bootstrap `disabled` instead of `ui-state-disabled`
Exclude frontend shim from docs build

Closes gh-3517
Allow specification of full highlight class in CSSHTMLHeader
Merge pull request #3523 from takluyver/docs-exclude-frontend

Exclude frontend shim from docs build

Closes #3517

The API doc writer has separate exclude patterns for modules and packages, so frontend needed to be listed in the modules exclusions.
Merge pull request #3516 from jakevdp/configurable_highlight

make css highlight style configurable
use `isoformat()` in jsonutil

allows preservation of timezone info.

Timezone info is still ignored in the extract-dates part, for now.
add IPython.utils.tz

Basic support for tz-aware UTC methods on date time objects.

The raw `utcfoo` methods still produce naïve objects,
so they are wrapped in a simple zero-offset tz-aware object.

This allows jsonutil to publish the timezone info,
eliminating the ambiguity of naïve timestamps (Firefox assumes local time, WebKit UTC).
add timezone info to `last_modified` in notebook managers

now Firefox won't get confused, turning utc timestamps into local times.

closes #3396
Add test for storemagic
Merge pull request #3506 from takluyver/storemagic_restore_aliases

%store -r restores saved aliases and directory history, as well as variables
allow just the trailing Z for timezone
ensure 'default' is first in cluster profile list

when sorting, `'default'` is transformed to `''`.
tweak regexp handling of tzinfo

allows for excluding the 'Z' from the timezone info
test jsonutil handling of dates
cleanup stale, unused exceptions in parallel.error

closes #2044