Custompath

Hi, this PR takes @thesli's comments and suggestions and packages them into a PR.

You can test this PR like this:

1) Clone couchdb-fauxton
2) `grunt release` to build the changes.
3) put together a test server:

package.json
```
{
  "name": "test",
  "version": "1.0.0",
  "description": "",
  "main": "test.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.9.8",
    "express-pouchdb": "^0.7.1",
    "morgan": "^1.4.0",
    "pouchdb": "^3.0.6"
  }
}
```

Test.js
```
var express = require('express')
  , app     = express()
  , PouchDB = require('pouchdb')
  , logger  = require('morgan')
  ;

app.use(logger("tiny"));
app.get('/', function(req, res, next) { 
  res.send('Welcome Traveler!  <a href="/express-pouchdb/_utils">Fauxton?</a>');
});
app.use('/custom', require('express-pouchdb')(PouchDB));

app.listen(3000);
```

To run the server with new Fauxton (assuming test and couchdb-fauxton are in same dir)
```
npm install
cd node_modules/express-pouchdb
mv fauxton fauxton.old
ln -s ../../../couchdb-fauxton/dist/release fauxton
node test.js
```

This addresses several issues identified and a couple extra.  From my testing, these issues remain, but none of them are show stoppers.  Compared to not working, 90% working is much better!

  - Databases -> Any DB -> Compact & Clean -> Cleanup Views -> "Error: missing" -> POST /custom//newdatabase/_view_cleanup 404
  - Databases -> Any DB -> All Design Docs -> Add Doc -> Hmmm... Adds regular doc.
  - Create Design Doc through Gear -> New View -> Design Doc Metadata

  - Url's have format like: GET /custom//_users -> double // isn't awesome.
  - API URL -> wrong url http://localhost:3000/newdatabase2/_all_docs  should include custom path. http://localhost:3000/custom/newdatabase2/_all_docs