Allow custom Metadata Key- Filters

[t0815]

Allow the user to define custom sets of quick access filters. When selected, only meta-fields defined in filter will be shown in the Datagrid.

• [x] add filter selection frontend controls to main window
• [x] add new form to manage and edit filters
• [x] apply filters
• [x] add filter base condition combobox

[t0815]

this was scheduled originally for v1.1, but i found it quite usefull -> so it will go to 1.0