Better labels for parameters

**Is your feature request related to a problem? Please describe.**
Currently labels for e.g. dispersion parameters are simply named: `epsilon_N` where `N` is the internal index depending on the order the interactions were created. This means that in the tabulated output of parameters, it is up to a user to keep track and work out what label maps to which interaction.

**Describe the solution you'd like**
Preferably, manually created potentials should use the atoms of the interactions as part of their label for easier identification. Also it should be possible to pass manual names into the constructor of interactions.

**Describe alternatives you've considered**
This may be rendered less important if/when #1350 is in. However, there is no sense delaying for that while this may still be useful.