Move python code to 'src' folder

[arky]

To aid packaging of the project, it is recommended to move all python code to "src" folder (ref python packaging guide). Putting the code in this structure and refactored as modules makes it easier to maintain and also port to multiple platforms.

This is require step before considering packaging EcoAssist to multiple platforms. #36

[PetervanLunteren]

Thanks for this tip :)