Clarify the 'detachment strength' effect of the Robust ability in other 'number of units' situations

[digi-brain]

As discussed in pull request #40.

The Robust ability text currently describes how the ability should affect the 'detachment strength' concept, given that the ability breaks the correlation with 'number of units'. (The detachment strength concept exists in the original of course — but as yet we haven't added the relevant content to the Battles or Armies components, where we will define this concept for Remastered.)

However, there are at least two other contexts where 'number of units' becomes ambiguous where the Robust ability is concerned:

• Relevant comment in relation to the Rally test
• Relevant comment in relation to the Leadership test

We've agreed that the same principle should apply in these situations — in essence, Robust units should count as two units in much the same way as we describe for the detachment strength concept. Probably the best solution is to replace 'number of units' in these contexts with 'current detachment strength'.

However, given that (a) we haven't defined that concept yet in Remastered, and (b) the Robust ability is still experimental at the moment, we decided that the best course of action for now is:

1. Stick with the unit-based phrasing for the moment.
2. Tweak/expand the experimental Robust rules text to make its effect in these other contexts plain as well. Or at least add a TODO note there so that we have a reminder and players have a pointer. (This issue is our prompt to do actually do this, probably on it's own discrete branch.)
3. Revisit if/when we add the other content and/or make Robust 'official' in future, and integrate as appropriate.