Exact mass calculation does not consider charge (electron mass).

**Requirements**

1. Determine the overall charge of a molecule (𝓷) by adding up the charges of all atoms.

> In this example:
>
> The overall charge is 𝓷=1+(-1)+(-1)=-1

2. When calculating `Molecular Weight` and `Exact Mass`an additional summand should be included: 𝓷*0.00054857990

> Mass of an electron taken from [here](https://physics.nist.gov/cgi-bin/cuu/Value?meu).

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**Steps to Reproduce**
1) Draw structure (e.g. ammonia)

2) Press `Calculated Values` button (or `Alt+C` key shortcut) --> `Exact mass` field value @ 7 decimal places: 17.0265487
3) Add positive charge ( --> e.g. ammonium) by using `Charge Plus` button

4) Press `Alt+C` again --> `Exact mass` field value @ 7 decimal places: 18.0343738
5) Calculate: 18.0343738 - 17.0265487 = result

**Actual behavior**
`Exact mass` field value @ 7 decimal places: 18.0343738
because system adds to ammonia mass (17.0265487) exact mass of atomic hydrogen (protium atom 1H - 1.0078251)

**Expected behavior**
`Exact mass` field value @ 7 decimal places: 18.0338252
because system adds to ammonium mass (17.0265487) exact mass of a protium atom (that is atomic hydrogen (1.0078251) without mass of an electron (0.0005486) = 1.0072765)

**Ketcher version:**
v3.2.0

**Additional:**
I guess this is based on the "Chemical Formula" in the "Calculated Values" already only having the chargeless "H4N"