[SysApps] Add the Storage Info data provider abstraction

This data provider was implemented differently from the CPU Info data provider.
I'm expecting the platform implementation to be more complex, so this is just an
interface.

The platform implementation should inherit from StorageInfoProvider and
provide a implementation of the static method GetInstance(). This will allow
the StorageInfoProvider[Windows|Tizen|Linux|...] to have its own attributes
and methods.
[SysApps] Make StorageInfoProvider observable

Add the Observer interface so other objects can get notifications when
a new storage is attached and detached.

It is important to remember that StorageInfoProvider must be a singleton,
so different webapps will share the same provider. This way, we don't waste
resources monitoring the same environment twice.

The provider will get a notification to start monitoring when the first observer
is added and another notification to stop monitoring when the last is removed.
[SysApps] Compile Chromium's StorageMonitor as a module

The StorageMonitor is almost self-contained, despite adding itself
to the Chromium's Browser Process. We should work upstream to fix that.

Meanwhile we can compile it as module (and protect the Chromium specific bits
with a flag) so we can use it as backend for the Device Capabilities
getStorageInfo() for Linux, Mac and Windows.
[SysApps] Add a data provider for Linux based on Chromium's StorageMonitor

This provider has a big chance of being generic enough to be used for Mac and
Windows. The backend for Android was not implemented yet which makes me sad.

We will have to implement a custom provider for Android (upstream maybe?).
[SysApps] Add stubs for Android, Mac and Windows

For Mac and Windows we just "forward" to the Linux implementation. There is no
buildsystem rule that includes all the ports but no Android.

The Android implementation is just a no-op that should print "not implemented"
warnings.
[SysApps] Implement the Device Capabilities getStorageInfo()

This patch implements the bits for retrieving the storage information. This is
not very diffirent for the getCPUInfo other than it is using a different
provider.
[SysApps] Add an method for checking if an Event is active

This is probably more straightforward than keeping booleans around
to check if there are listeners for a certain event.
[SysApps] Make DeviceCapabilitiesObject an EventTarget

This patch adds the native bits of the EventTarget. This will allow
DeviceCapabilitiesObject to get notifications when there is someone listening
for events, so we can start monitoring the filesystem by adding an observer.

It is important to notice that it will only add itself as an observer to the
StorageProviderInfo when there is actually some listener in the JavaScript side,
this way we don't do any monitoring if nobody is listening.

The EventTarget class triggers the StartEvent() method when the first listener
is added and the StopEvent() when the last listener is removed for a particular
event.
[SysApps] Make the JavaScript shim dispatch events

The first thing to be done is make the JavaScript DeviceCapabilties an EventTarget
(which is also a BindingObject). The BindingObjects are JavaScripts objects with
a link with some native object and they use a unique ID for routing messages
between them.

common.EventTarget.call(this) initializes the EventTarget and makes
this._addEvent() possible.

Now all the blanks are filled and we are good to go. The next step would be
replace the StorageInfoProviderMock with a real implementation for each platform
we support. No need to touch on anything else.
[SysApps] Implement the Device Capabilities getMemoryInfo()

This is probably the easiest to implement and the most portable API. It could be
implemented without a "provider", but let's just keep using the pattern to make
the implementation more coherent.

We are using the Chromium abstractions, so it should work on all platform
supported by Chromium with no need of provider abstractions.
[SysApps] Implement the Device Capabilities getDisplayInfo()

This provider is missing an Observer interface for notifications
of displays being connected and disconnected. This is very likely to
be platform dependent and we might need to add platform files.

Currently we only using a static method, but I'm keeping the GetInstance()
for the display monitoring implementation.
[SysApps] Watch for displays connections and disconnections

Using the Chromium's gfx:: abstractions on top of Screen and Display,
we can watch for new connections and disconnections in a portable way.

This patch also adds an observer interface to DisplayInfoProvider so
the DeviceCapabiltiesObject can subscribe to this events when necessary.
[SysApps] Dispatch display events to the JavaScript shim

Connect the bits from receiving a display connection/disconnection
event from the system to sending an event message to the JavaScript shim.

It is important to remember that the event is only triggered if there are
event listeners waiting for it.
[SysApps] Added a mock StorageInfoProvider

This is just a mock info provider emulating how a provider will behave in a real
life. When monitoring for file system events, it will add and remove a storage
every 1s. It will also report at least 3 non-removable storages when asked.

We could reuse this later for unit tests.
[SysApps] Do not build Device Capabilities for Tizen and Android

Otherwise it will clash with the new implementation.
[SysApps] Add a simple test for Device Capabilities

Not to self: make a browsertest out of this. :)