Make plots prettier

[joewandy]

1. The two bar plots in the show motif page are super ugly .. Could easily redo them using plotly?
2. Intensity plot, maybe better to show in log scale

[joewandy]

Also see #138

The fragmentation spectra plot could be improved:

Load each spectra from server when the user clicks next/previous, rather than preloading all the data at once.
Add zooming/panning
Display neutral losses on the plot
Display feature annotations from e.g. Magma.