Unified server/desktop config

All,

Attached is a patch that aims to allow us to have a standardised config
that will work out of the box for both web and desktop modes. It does this
by doing two things:

1) The runtime sets SERVER_MODE in the Python environment before starting
the app. If this value is set, then it overrides the default value of
SERVER_MODE in the config.

2) The config file then offers default values for the various file
locations for both server and desktop mode, setting them appropriately
based on the derived SERVER_MODE value.

The only downsides I can see from this are:

- You cannot run in server mode in the runtime without manually
reconfiguring SERVER_MODE and likely a bunch of paths in config_local.py

- If you want to override SERVER_MODE, you'll probably also need to
redefine the various paths in config_local.py.

I don't see either being something 99.9% of users would need though.

Can anyone see if the patch breaks anything, or if I missed any side
effects?

Is it likely to break things during upgrades? I suspect so... so maybe this
should prompt v2.0?

I'd appreciate multiple reviews of this, as it could break things. Note
that I haven't yet updated the docs.

--
Dave Page
Blog: http://pgsnake.blogspot.com
Twitter: @pgsnake

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