Add checkbox to all listing to select/deselect all

[rochecompaan]

In our listings (eg orders, invoices, valuations, etc and not the project views), add a checkbox to the left of all column headings and to the left of each row to select/deselect all records - refer to toggl's ui for this.

[nvernooy]

@rochecompaan, the Valuations, Claims, and Payments listings do not have a ctrl-click selection model. Should I add that to those listings as well as the checkboxes?