revid: simplify config.Config field types

[Saxon Milton]

This is in preparation for changes to be made to achieve issue #241.

Firstly, considering that a lot of configuration is done using constant string literals, we may as well have the enum fields in the Config struct e.g. Input (can be File, Raspivid, Webcam etc) just be string literals instead of uint8 consts. This will reduce the need for conversion from the map[string]string we get from the cloud, to the config.Config struct. As well as this, our enum consts for Inputs and Outputs etc should also just be string literal values, then we can easily compare to Config fields in logic.

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Secondly, integer fields in the Config struct should all be int.

[Ella Pietraroia]

Saxon

[Saxon Milton]

We are going to approach this differently.