Fixed tabbing between inputs in a block
Used the startEditing() method

The old code was doing incorrect things for empty text fields.
Switched end condition
Fixed tabbing for blocks with nested reporters
Switched to a do…while loop
Switched to a tabbing algorithm which crosses boundaries between blocks
Made tabbing algorithm handle command blocks nested as arguments
Merge pull request #285 from nathan/script-tabbing

Fix tabbing between inputs in a block