Improvements: keyboard shortcuts, offline workspace init, and more

[swtyree]

Hi all, thanks for this wonderful tool. Here are some changes that I made while using it for an annotation project:

• Added keyboard shortcuts to the GUI for moving forward/backward by 10 frames (shift+arrow) and to the start/end (option/alt+arrow)
• Added keyboard shortcuts for committing a frame to permanent memory (C), propagating forward (F/space) and backward (B), and quitting the GUI
• Added command line flag --workspace_init_only to initialize the workspace (including importing images or video) and then exit without creating GUI
• Documented these in TIPS.md and INTERACTIVE.md

Finally, a couple minor fixes/edits:

• Changed GUI to look for TIPS.md in the appropriate source path, instead of relative to pwd (without this, the GUI will crash if not launched from the root directory of the repo)
• Moved some imports and hydra initialization to after parsing command line args to make --help print faster

Let me know if you need anything from me to help with merging these changes. Thanks!