Usability Enhancements

Two little improvements to make your Acunote life easier:

1. First one is for those of you who use full power of the Acunote's keyboard shortcuts. We have added two new shortcuts for task selection: * then a - select all tasks, * then n - deselect all tasks

2. The next one is multiple selection with shift+click. I hope this one will make task organizing much easier. Enjoy