libcore|App: Accessing persistent data in read-only or mutable mode

Timestamps get updated automatically if the Archive is accessed in
mutable mode. Fixes a problem with Refuge (Config) where timestamps
were not being preserved even though no one had written to the archive.
libcore|Config: Check config script's package's timestamp

If the packages have been updated, read the config script just in
case. This makes things easier for developers when the scripts are
changed but the app version hasn't.

Added some utility methods to Package for finding the container
package of a file and checking its timestamp.
Client|UI: Auto-hide the alert notification (default: 3 mins)

The config variable is 'Config.alert.autoHide'.

IssueID #1848