Made the apps list refresh when apps modified out of e:t

This is so that when elegant:tab is opened, and if the user installs,
uninstalls, enables or disables an app, the apps list will refresh so the
user will not see an outdated one.

Added trimming of local storage for top site thumbnails

The storage will be trimmed whenever the new tab page is loaded. Since
the top sites constantly updates, there might be thumbnails that might
not be shown. These are removed from the local storage.