More complete tests of FormatterUtils.
More tests of anonymous object support.
More robust test methods

- Added anonymous types to the test repertoire.
- Normalised test failure messages to specify the exact cell reference.
- Minor refactoring to use simpler constructs where possible.
- Expanded a few test cases.
Removed cell height. :(

The cell height features in EPPlus are completely unreliable, so I have
no choice but to remove this feature. I might try to fix this bug
myself, if I get a chance.