Application storage should not cache all installed applications data

Since we dropped "Main document" functionality there is no need for
Application storage to cache all installed applications data, besides
doing so uselessly wastes memory.
Another goal of this patch is preparation Application storage for accessing
it from other processes than browser process (e.g. from xwalkctl process)
and for using different Application storage implementations.
Merge pull request #2119 from pozdnyakov/Refactor_ApplicationStorage

Application storage should not cache all installed applications data