Build system update

This pull request moves the each of the build targets into a JSON manifest and adds several build configuration options.

# Invoking Build System

Prerequisites for running this script include BeautifulSoup and Jinja2. You can install them both with:   
`sudo easy_install beautifulsoup4 jinja2`

This assumes you have python-setuptools:  
`sudo apt-get install python-setuptools`

Once you have everything setup, you can run the build with:

`python build.py` and optionally select build targets as below.

# Options

These command line options determine which applications get built.

`--platform=chrome` builds all files with no targeted platform or targeted for Chrome/web.

`--platform=web` (default) builds all files with no targeted platform or targeted for web.

`--release=experimental` builds all apps regardless of release status

`--release=deprecated` builds all apps that have had an Alpha (or better) release.

`--release=alpha` builds all apps that are in Alpha (or better).

`--release=beta` builds all apps that are in Beta or released.

`--release=release` builds all apps that are released.

# Manifest file format

Applications in privly-applications are built by specifying the manifest.json document as found below.

    [
      {
        "release_status": "alpha", // Required values: experimental, deprecated, alpha, beta, release
        "platforms": ["chrome"], // Optional values: web, chrome
        "subtemplate_path": "Pages/ChromeFirstRun.html.subtemplate", // Required path to the subtemplate
        "outfile_path": "Pages/ChromeFirstRun.html", // Required path the othe output file
        "subtemplate_dict": {"name": "FirstRun", "action": "nav"} // Template dictionary values
      },
      {...}
     ]