[SysApps] Compile StorageMonitor as a component

So we can compile it as a module for Crosswalk and use it as platform
abstraction for the Device Capabilities getStorageInfo() API.

This is being worked upstream at and got a green light to proceed:
https://codereview.chromium.org/152343005/

It will probably not be necessary after next time we bump Chromium.
Merge pull request #117 from tmpsantos/storage_monitor

[SysApps] Compile StorageMonitor as a component