Update database schema/entities diagram, update README point to docs

Squashed commit of the following:

commit 6247fae507b5e455c00e2eb510eb0b9fa1d7d723
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Dec 15 09:22:11 2014 +0100

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commit a116a44265783b83c6e00fed6756c9f1b7ef3fb5
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Dec 15 09:21:10 2014 +0100

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commit 4d544cc4d2a2b6bd0f4f3fb2bdce63c7204ca946
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Dec 15 09:18:26 2014 +0100

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commit bc9c183b5a3d809addb8ae6ea9fda3a9856d99c2
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Dec 15 09:06:11 2014 +0100

    Update database schema / entities diagram