Add themes + components to reports

Allow theming for reports rather than the single theme we have now. Can switch the theme with Report(theme='gwdetchar').

Also add two components to the report, having elements similar to the detchar summary pages:

• ImageBoard
• FlatTable

Unfortunately the names could be better, but wanted to keep backwards compatibility with the existing ImageGrid and Table components.

As an extra, remove the clock from the reports as it doesn't add any value and is distracting.