Implement considerations for Relax within osu!taiko diffcalc

[Lawtrohux]

There's really not much to this. Implements considerations for relax.

• Makes Relax incompatible with Swap and Random, as this is redundant with no colour in relax.
• Relax gives 0 rating to colour, a harsher scaling for converts, and a divided stamina difficulty due to the assumed increased finger count.

Shouldn't need a sheet or anything, as it is purely RX based.

[Lawtrohux]

This will need to go in before the major pr, so i can merge conflict accordingly.