add more cli power (multiple task updates, incremental importance/effort/due)

[ardunn]

should be able to:

dex task e* imp 4

To set all tasks in project e to importance 4. Also,

dex task e1,e4,e9 imp 5

Should set those specific tasks to imp 5. Also,

dex task e* imp +1

Should increment the importance of the tasks selected.