Use temp feature bits for splicing and 0FC

[TheBlueMatt]

These aren't yet standard and may be subject to change, so 0.2 should use temp feature bits.

[TheBlueMatt]

Also the HtlcHold feature bit.

[valentinewallace]

For HtlcHold, done in #4045

[TheBlueMatt]

This is done for 0FC and HtlcHold. Now we just need to decide if we're gonna do it for splicing or if we're gonna do cross-compat enough this coming week to Just Ship It. Doesn't need to happen for the beta tho.