Show effective bf in decay chain viewer

[vvsagar]

Follow-up from enhancement #561.

[vvsagar]

Hi @eduardo-rodrigues, this is just a simple PR on top of the previous one. No hurry to merge it at all, I am working on other things in parallel anyway. Wish you a nice Easter break :)

[eduardo-rodrigues]

Hi. This update looks good, though I see some changes in the notebooks such as

-      "        new Lineshapes::RBW(\"rho(770)0\", rho_770_0_M, rho_770_0_W, 1.0, M_12, FF::BL2),\n",
+      "        new Lineshapes::RBW(\"rho(770)0\", rho_770_0_M, rho_770_0_W, 1.0, M_34, FF::BL2),\n",

, which I do not understand. I let @henryiii comment since this relates to his contributions ...

Could you also paste a visualisation example with your enhancement? That's useful.

Many thanks.

[vvsagar]

Oh yes, I added a visual example in the notebook I modified but I forgot that for ipynb files, diffs are not visualized.
You can see it here in the source branch in cell 17: https://github.com/vvsagar/decaylanguage/blob/feature/show-effective-bf-DecayChainViewer/notebooks/DecayLanguageDemo.ipynb

[eduardo-rodrigues]

I see now that @henryiii gave a 👍. We're good. Merging.