Add measures at package level

This is an intermediary view level between project/module and classes.

Example : complexity is too much high on project FOO, particularly on packages com.foo.bar and com.foo.baz.

• In a project without modules we should display a treemap based on packages metrics
• From that treemap, it should be possible to click on a package and to zoom in that package
• The package level must be inserted in the Breakdown services (Measure and Coding Rules)

In the "Coding Rules Breakdown":

• the first column will contain Level, Category and Coding Rules
• the second column will contain Modules and Packages
• the last column will contain Classes

In the "Measures Breakdown":

• the first column will contain Measures
• the second column will contain Modules and Packages
• the last column will contain Classes