JR - Add muzzle slots for 4.6mm and 7.62x54R

[Blutze]

When merged this pull request will:

• Add one single muzzle slot for 4.6x30mm, should cover both the MP7 and the UCP (if anybody ever makes one)
• Add two separate muzzle slots for 7.62x54R, one for SVDs and one for PKs; closes Joint Muzzle for 7.62x54R and/or SVD rifle #1226.

Potential TODO
- [ ] Remove DMR_01 from legacy JR component
- [ ] Add new SVD muzzle slot to DMR_01

• close Joint Muzzle for 7.62x54R and/or SVD rifle #1226

[Blutze]

Just tried screwing things onto that weirdo bullpup Dragunov. BI might have intended this to be an "SVD muzzle", but stopped short of declaring a standard for proxy positioning.

srifle_DMR_01_F
rhs_weap_svdp
rhs_acc_tgpv
rhs_acc_tgpv2

If someone makes an SVD suppressor that matches the proxy position on DMR_01 we can revisit this, but for now I'll just add the JR slot itself.