Add commands to navigate by groups. Add cycling to commands.

[okamsn]

• Add option selectrum-cycle-movement. When enabled, navigation
  commands wrap around. Requested in Is it possible to enable cycling? #570.
• Add commands to navigate by groups (with optional cycling).
  Requested in Previous / Next group navigation for multi-sources #554.

[okamsn]

@minad In the Selectrum README, the comparison with Vertico has the sentence

On the other hand, Vertico additionally supports cycling over candidates and provides more commands for grouping support.

Since you are more familiar with Vertico and Selectrum than I am, I ask whether you are content with removing this sentence in this PR or if you would like to see it changed. Do you have any thoughts/preferences on this?

[minad]

@okamsn Yes, it makes sense to update the Vertico/Selectrum comparison. Note that Vertico has changed a lot recently, so removing that sentence will not lead to a description which correctly reflects the status quo. So maybe updating the description should be done in a separate PR. Vertico acquired many more features due to its extensions. The main issue with Selectrum is that it doesn't implement support for dynamic completion tables correctly and has multiple other compatibility issues (#114, #481, #532). This was the main reason why I started to experiment with a new implementation, which then turned into Vertico. See also https://github.com/minad/vertico/#alternatives. (EDIT: For more background see also the thread in #532, where we discussed about dynamic completion tables and I started with a prototype implementation originally called minicomp.)

[okamsn]

OK, I've left the comparison unchanged in this PR and created issue #589.