Added reports module initial structure
Added abstract report module class and template
Added abstract sales report class and product sales report implementation
Improved labels and CSS of backend report module
Improved product sales report
Added icons for reports.

A commercial license will follow so everyone can use Isotope in
a commercial environment (as obviously everyone does).
Added abstract classes for report ideas

These are currently just ideas what reports should be available.
There's probably a lot more to come.
Confirmation of commercial license for the icons
Show a daily summary on the reports overview page
Moved date parser to separate method
Added method to get filter-by-config panel
Each data value can be an array and will then be imploded with line break
Implemented sales total report, added MilkChart library
Use report description as default headline
Show 0 sales total if no results are found
Fixed legend labels
Added group permission settings
Do not show empty currencies in the chart
Limit the report data to the allowed product IDs
Use full textual representation for month name