Various documentation, package description tweaks, and minor fixes

Also one small fix for the client metadata extractor test.

I have reformatted the README as reStructuredText as the Markdown version doesn't look so great in the [Python Package Index](https://pypi.python.org/pypi/girder/0.1.22): 

I have added a configuration file for [Bower](http://bower.io) (```npm install -g bower```), which is like NPM but for front-end web assets. For instance, in future, instead of copying dependences into this repo, we could add:
```json
{
...
"dependencies": {
    "bootstrap": "~3.2.0",
    "bootstrap-switch": "~3.0.2",
    "d3": "~3.4.11",
    "jquery": "~1.11.1"
  },
...
}
```
@jamiesnape Let's move this to requirements-dev.txt.