nbconvert tests

# nbconvert tests

## Overview

Suite of automated nose tests for nbconvert.  Adds **67** tests specific to nbconvert (not all listed below).
**Accompanies #3607**

## Done

- Travis CI

### App tests

- Does help show when no notebooks are specified?
- Does glob work?
- Does glob into a subdirectory work?
- Does explicit notebook listing work?
- Does glob, then explicit notebook listing work?
- Does explicit notebook listing and then glob work?
- Does default config work?
- Does custom config via commandline override directory config?
- Does the format specified from the commandline override format in default config?

### Exporters

- Try export by name with a name we know doesn't exist, do we get the right error?
- export_by_name a filename
- export_by_name a notebook node
- export_by_name a filestream
- export using an exporter instance
- export using an exporter class
- Try to export with resources, does it still work?
- Try to export without an exporter, does it through the right error?
- Try to construct an exporter
- Try to construct a basichtml exporter
- Try to construct a fullhtml exporter
- Try to construct a latex exporter
- Try to construct a markdown exporter
- Try to construct a python exporter
- Try to construct a reveal exporter
- Try to construct a rst exporter
- Try to construct a sphinx_howto exporter
- Try to construct a sphinx_manual exporter
- Export using an exporter
- Export using a basichtml exporter
- Export using a fullhtml exporter
- Export using a latex exporter
- Export using a markdown exporter
- Export using a python exporter
- Export using a reveal exporter
- Export using a rst exporter
- Export using a sphinx_howto exporter
- Export using a sphinx_manual exporter
- Try enabling the extract figure transformer, verify figures are extracted
- Try adding a custom transformer via the extra transformers list (instance)
- Try adding a custom transformer via the extra transformers list (class type)
- Try adding a custom transformer via the extra transformers list (dotted object name)
- Try adding a custom transformer via the public method

### Filters

- DataTypeFilter

#### ansi

- remove_ansi
- ansi2html
- ansi2latex