provide explanation when number of files is greater than number of classes for a package

There might be a case that number of files > number of classes listed:

This is normal behaviour, because by default Clover hides entities having no executable code, such as: empty classes, enums (with no methods), interfaces (with no virtual extension methods).

However, this may be confusing for end user.

How we could improve this:

1) Set the showEmpty to true by default. Benefit: 'classes >= files' in all cases. Drawback: report will contain unnecessary noise.

2) Add [(?) Help] button above the table. Example:

3) Add tooltip for 'Files' (TotalElements.getHelp())

4) Add small text below the class table. For example:

"3 classes are not listed because they contain no executable code."