Add system updates installer in installation.app

[louies0623]

It's like every iso of beta version of windows has an upgrade program on the installer.
Like Mac OS installer

[probonopd]

FreeBSD (minor versions) and its packages can be updated using Update.app (in "Under Construction").

As for upgrading the whole system, please refer to #55. We need a fool-proof and robust upgrade/update strategy first before we can implement anything.

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