Add 60 key layout for Sofle

[titus-ong]

Hello, I created this for my Sofle keyboard, might be useful for others so I created this PR.

[urob]

Thanks for committing the PR! I'd probably use a slightly different naming scheme:

╭─────────────────────────────┬─────────────────────────────╮
│ LN5 LN4 LN3 LN2 LN1 LN0     │     RN0 RN1 RN2 RN3 RN4 RN5 │
│ LT5 LT4 LT3 LT2 LT1 LT0     │     RT0 RT1 RT2 RT3 RT4 RT5 │
│ LM5 LM4 LM3 LM2 LM1 LM0     │     RM0 RM1 RM2 RM3 RM4 RM5 │
│ LB5 LB4 LB3 LB2 LB1 LB0 LEC │ REC RB0 RB1 RB2 RB3 RB4 RB5 │
╰───────╮ LH4 LH3 LH2 LH1 LH0 │ RH0 RH1 RH2 RH3 RH4 ╭───────╯
        ╰─────────────────────┴─────────────────────╯

This way, the "core alpha" keys will be consistently named across the other keypos definition files. So someone who has a 42 key corne and a Sofle can switch between them, and all the core keys will be the same. E.g., the home row keys will always be LM5 to RM5.

(The 58keys layout is an exception to this pattern, which I had missed when merging. It really should have had a numbers row added, instead of shifting all the other rows up.)

[titus-ong]

Ah yeah that makes sense, I was wondering why the 58key layout was named as such. I've fixed it in the latest commit.

[urob]

Great, thanks!