Add decfiles for sexaquark analysis

Add various dec files for Sexaquark decay modes and corresponding backgrounds.

Included are

• \Xi_b^{\prime -} \rightarrow \Xi_b^0(\rightarrow S \bar{p} K^+) \pi^-
• \Xi_b^{\prime -} \rightarrow \Xi_b^0(\rightarrow S \bar{p} D_s^+) \pi^-
• \Xi_b^{*-} \rightarrow\Xi_b^0( \rightarrow S \overline{p}K^+) \pi^-
• \Xi_b^{*-} \rightarrow\Xi_b^0( \rightarrow S \overline{p}D_s^+) \pi^-
• \Sigma_b^{\pm} \rightarrow \Lambda_b^0( \rightarrow S \overline{p}K^+) \pi^{\pm}
• \Sigma_b^{\pm} \rightarrow \Lambda_b^0( \rightarrow S \overline{p}D_s^+) \pi^{pm}

and for each mode the 2 main BGs where the S is replaced by \Lambda \Lambda or \Xi n

as well as three modes with a JPsi in the final state

• \Xi_b^{\prime-} \rightarrow \Xi_b^0( \rightarrow SJ\!/\!\psi \overline{p}\pi^+) \pi^-
• \Xi_b^{* -} \rightarrow \Xi_b^0( \rightarrow SJ\!/\!\psi \overline{p}\pi^+) \pi^-
• Xi_b(5945)^0 \rightarrow \Xi_b^- (\rightarrow SJ\!/\!\psi \overline{p}) \pi+