Calculator Feature Updates -- mostly for multi-wavelength useability

[Tohuvavohu]

• Allow easy user input of big/small numbers in the Depth field for calculator
  eg: Limiting flux in unit erg cm-2 s-1 for typcal x-ray telescope followup is <1e-11. Currently the field only allows purely numerical input.

• Extend 'Depth Unit' dropdown to have more multi-wavelength friendly options eg 'Jy' . We probably need to think a little harder about use cases here.

• Restructure the panel that has the input/drown fields for calculator, so that the spectral coverage features are clearly clustered together and separate from eg 'Approximate' and instrument fields.

• More documentation/tooltips for each field.

• Make it so that your field entries don't vanish when you click 'Calculate', retain them on page for use reference.

• Consider labelling the produced coverage plots with input parameters?

• Fix so that 'waiting' bar does not become arbitrarily long when waiting on long calculations