Remove unused code in bin
extract reporter to top level

This allow to run sevela instances of mocha and keep hand on repoters
behavior.
Update testscript to test function extensions
Add a project-name option
Add client should end automatically
Prepare to extract mocha runner as a runner among other
[WIP] Migrate screenstory to webdrivercss

[X] Capture with webrdrivercss
[X] Store screenshots in `--screenshot-root` argument path
[X] Forward to [webdriverxss-adminpanel](https://github.com/webdriverio/webdrivercss-adminpanel)
[X] Add command line option to use **adminpanel**
[X] Scope by stories in **adminpanel**
[X] Add `--screenshot-width` and `--screenshot-orientation` client options
[X] Screenstory should expects base64 strings with images
[X] Add generated images to screenstory report
[X] Automatically load screenstory.yml files
[] Update readme
[] Generate a report with only images that differs.
[] Use webdrivercss `saveDocumentScreenshot` method

Capture With Webdrivercss
-------------------------

Replaced the `capture` function in screenstory extension.

Forward To webdriverxss-adminpanel
----------------------------------

* Add a cli option `--admin-panel` to pass an admin panel url.
* Use this option in screenstory extension to initialize webdrivercss
* Update package.json test script

Scope by stories in **adminpanel**
----------------------------------

Use `--project-name` and story title as prefix.

If no project name is given, nor story title, a default project name is
used.

Generate a report with only images that differs
-----------------------------------------------

A new report should be generated with tests that failed.

It should handle states of image (created, removed, updated)

Add an option `--config-file`
-----------------------------

Load a yaml file with configuration options.
It should accept all the command line available options.

Report update
-------------

Screenstory now fully relies on webdrivercss for screenshots.
It provides updated informations to template. Default image url is:

* diff file when modified
* current when unchanged

Image has following informations:

* browserId:     unique id for given capabilities
* fileOriginal:  the path to original screenshot file
* fileNew:       the path to new screenshot file
* fileDiff:      the path to new screenshot file
* urlOriginal:   the path to original screenshot file
* urlNew:        the path to new screenshot file
* urlDiff:       the path to new screenshot file
* isNew:         is it a new screenshot for those capabilities
* isModified:    is it a new screenshot for those capabilities
* diff:          webdrivercss response
* capabilities:  the current client capabilities ("client.desiredCapabilities")
* title:         the image human readable title
* story:         the story human readable title
* id:            the image unique id. Maybe best to keep it generated by screenstory.
* storyId:       the story unique id. Maybe best to keep it generated by screenstory.

screenstory.yml
---------------

Define capabilities alias for your project.
Defaults are located in screenstory's root directory.

Added  capabilities for saucelabs and browserstack