SLAB alternate stock & sidepanels

Very simple alteration of the original files to add more tactics to the slab.

 I used this model by sigstoat for the rail parts and made the dartholders myself in fusion360. The slab files are from sillybutt's github page

The picatinny parts are yet to be tested. The dartholders work well for worker 3+ darts, but elites will fall out if you shake it to hard. 

Update 09.07.23:

• Added sidepanels with dartholders as requested. There's a version that holds 3 darts and a version that holds 4 darts.
• Uploaded dartholder model for easier remixing.