UX Improvement: Add a hotkey to auto-confirm a region's label

[joshuahaddad]

Currently you can select a default class by selecting a class from the Label List, draw a region, hit enter and the labeling dialogue box will be auto-filled with the default class. However, hitting enter again does not accept the label dialogue box. Instead, hitting enter after opening the label dialogue box will change the class to the first label in the list and hitting enter again will accept the label. This combined with the dialogue box not intelligently positioning (allowing it to appear clipped near the bottom of the screen) slows down labeling of large numbers of the same object.

It would be very helpful to make hitting Enter after opening the label dialogue box accept the label, rather than interact with the label selection portion of the dialogue box.