Include labels for the transitions

[leandro-liborio]

Is your feature request related to a problem? Please describe.
In the input file or main Galaxy GUI, we can chose the transition or transitions for which energy and rates are desired. For instance, for the muonic Cu, we can chose M4-N6, M5-N7, L2-M4, L3-M5, L2-N4. This will result in a series of peaks in the spectrum.

Describe the solution you'd like
Is it possible to label the peaks in the spectrum with their corresponding transition?

Additional context
For instance, in this spectrum for muonic Cu, from left to right, the labels would be: M4-N6 and M5-N7; L2-M4 and L3-M5; L2-N4