Allow inline currency conversion input

[ghost]

Cone version used: Version 0.2.20

Hi there,

Is there a chance to put inline currency conversion into the list of future features?

Here is one example of what i meant by that

2020-05-04 * Conversion
  Pocket            EUR 10,00 @ USD 1.10
  Bank

This can quite be good since it works in ledger-cli and it is super convenient to convert and write down rates right away instead of defining changes right before you move your property between accounts.

So far, cone is allowing only numbers in that input field.