Show only active tasks in the overview view

Active tasks are unbilled tasks that are tasks that are either fixed cost
or that have time entries that should be billed.
Show a total of unbilled time and earned money (excl. VAT) per customer
Build a span per customer so that they flow and use two columns in the overview
Ignore style.css.map generated by Sass
Merge branch 'feature/02ad0e-improve-main-overview' into development (closes: #02ad0e)