Remove all white spaces
[apache] Update the `Custom 404 page` section

- Provide a more meaningful description.
- Comment out the `ErrorDocument` directive as this project doesn't
  offer the custom 404 page like other projects do.
[apache] Remove `php_flag register_globals Off`

The `register_globals` directive is not required anymore as it
defaults to `off` starting with PHP 4.2.0, is deprecated as of
PHP 5.3.0 and removed as of PHP 5.4.0:
http://www.php.net/manual/en/ini.core.php#ini.register-globals

Also, support for PHP 4 has been discontinued since 2007-12-31:
http://php.net/releases/index.php
[apache] Add comment about font MIME types

Browsers usually ignore the font MIME types and sniff the content but,
Chrome, shows a warning if TrueType / Opentype fonts aren't served with
the `application/x-font-ttf` / `font/opentype` MIME type.

References:
* h5bp/html5-boilerplate#1317
* http://mimesniff.spec.whatwg.org/#matching-a-font-type-pattern
[apache] Remove all `php` configurations

The php directives have been included in the Apache hypertext access
file more as helpful information then to be used out of the box.

Nowadays, the use of the directives is highly dependent on the php
version and the way in witch php is integrated with Apache. This makes
them less usefull by default and just extra code to remove for both
the people that don't use php and the ones that do (especially a newer
version).

Reference: h5bp/server-configs#140
[apache] Update code comments

* Provide more meaningful comments and remove the superfluous ones.
* Remove / replace outdated URLs.
[apache] Group related sections together
[apache] Consistency changes

* Use consistent code indentation (4 spaces, 2 seems cluttered).
* Maintain the same arrangement style for all group directives.
[apache] Add `Open Web App manifest` configs

An Open Web App manifest file (having the extension `.webapp`):

* must be served with a `Content-Type` header of
  `application/x-web-app-manifest+json` (this is currently not enforced
  by Firefox but is enforced by the Firefox Marketplace while, Firefox
  OS only checks this if the origin of the page where the user triggers
  the install is different from the origin of the app itself)

* must be UTF-8 encoded in order to be submitted to the Firefox
  Marketplace

* should not be cached (the expires headers for the manifest are usually
  ignored by Firefox but, just to be sure):

  "Webapps.jsm <http://mxr.mozilla.org/mozilla-central/source/dom/apps/src/Webapps.jsm>
  sets INHIBIT_CACHING <http://mxr.mozilla.org/mozilla-central/source/netwerk/base/public/nsIRequest.idl#141>
  when it downloads the manifest, which prevents Firefox from caching it
  so, in theory the Firefox app runtime won't take expires headers into
  consideration. However, INHIBIT_CACHING doesn't prevent the runtime
  from using an entry in the cache if it exists so, if you load the
  manifest yourself, f.e. to see what it looks like, while developing
  your app, Firefox might cache it, and Webapps.jsm might then get the
  cached version.
  ...
  Webapps.jsm is the implementation of the DOMApplicationRegistry that
  is responsible for managing app records, including their manifests"

                            ~ thanks to @mykmelez for the explanation ~

* is a JSON file so, it can be compressed (the manifest validator
  <https://marketplace.firefox.com/developers/validator>, doesn't seem
  to mind)

* doesn't need any of the extra headers (e.g.:`Content-Security-Policy`,
  `X-UA-Compatible`, etc.)

Reference: https://developer.mozilla.org/en-US/docs/Apps/Manifest