Add "unclear" or "to be checked again" column

[matgille]

Related in some way to #29

Is your feature request related to a problem? Please describe.
Sometimes a token is difficult to analyze; the correction needs to be checked by other team members (or to be verified later by the same person). It would be usefull to be able to highlight in some way these tokens.

Describe the solution you'd like
I think of a new column "to be seen again" or "unclear". A new quick link would list all of the unclear analysis; add a specific background color ?

[PonteIneptique]

Nice feature that is indeed some form of changes of #29

Two ways to implement:

1. Add a new property onto tokens directly (update WordToken table)
2. Add a new table which connects to tokens (might be lighter to handle as well ?)

[PonteIneptique]

Juliette, when you have time (so not now), this is a good feature to add.