Add a way to select multiple include directories at once when setting up a project from compilation database

[ffuugoo]

This is frustrating a bit:

AFAIK some (all?) Windows apps do it like this:

• ctrl-/shift-select multiple lines
• check/uncheck a checkbox on any selected line
• checkboxes of all selected lines get the same state as the clicked one

This is kinda counter-intuitive, but this will get the job done.

[egraether]

Fixed with 0.8.20
Allow line selection with SHIFT and added buttons for select/unselect all/selected.