Add /history command

[TimJentzsch]

Add a /history command to see the history of transcriptions made by a user.
This would work similar to the !history command of the old bot as detailed in #11.

Example response of the old bot:

It shows a plot of the user gamma in relation to the time. Additionally, the rank milestones are visible as lines on the graph.

Options:

• user 1 (optional): The user to get the history graph for. Defaults to the user executing the command.
• user 2 (optional): The second user to plot alongside the first one. Defaults to none.
• user 3 (optional): The third user to plot alongside the other ones. Defaults to none.

[TimJentzsch]

This could be implemented like this:

1. Get the current gamma of the user via the volunteer endpoint.
2. Get the transcriptions of the user via the transcription endpoint. For each page of transcriptions, do the following:
   1. Calculate the current gamma at the point of each transcription with the help of the total gamma count of the user
   2. Add the times and the gamma counts to a list of data points
   3. Plot the datapoints with pyplot, in addition to the milestone lines
   4. Update the response to the user with the current graph

This is not very efficient and might take a while for users like Cloakknight, but the iterative updates ensure that the user quickly gets a response.