Improve logging capabilities and coverage

[hayfield]

In the early days of pyIATI there was a grand idea that there would be significant logging of things that happen. This grand idea faded quickly as other shinier things moved to the top of the priority list.

The initial implementation of logging functionality involved adding a small number of functions to the utility module: https://github.com/IATI/pyIATI/blob/v0.3.0/iati/utilities.py#L273-L345

---

A very-high level approach that could be taken to solve this:

• Assess the features of the Python logging module
• See what logging features are desired across pyIATI as a whole
• Examine the current approach to see whether it's at all suitable
• Develop a robust logging system and scale it across pyIATI as a whole

It may be desired to investigate this in conjunction with error handling (see: #240).