Initial Shepherd implementation

[IanMayo]

Fixes #90

[IanMayo]

Good work @Morphexe

Feedback:

• can you make the very first screen 50% wider? That will let it fit on the screen better.
• step titled "the earlier steps shows how the timestamp...". We've missed out steps 5-8.
• step titled "Finding data". We need to display this to the right of the target, since it obscures the drop-down lists.
• final step "Future plans". Not displayed.