Improve the stats output that TeX bot produces

As it says on the tin. There are a few issues that I have noticed with the stats the bot produces that I think improving on could help the bot look somewhat cleaner on:

**Removing redundancy**
When a user uses the `/stats self` command there is some level of redundancy. If a user does not have many contributions they will end up with bars of height 0:

Fixing this may also prevent some security issues - we can see an example of this in the above output, where despite not being on committee, the bot has shown me some committee channels that are available.

**Make text less cramped**
Here is an output from the `/stats server` command:

As one can see the text is quite cramped. It also displays committee only channels, which server admins may not want users to see depending on the application of the bot. I would also like to fix the margins so that all the text fits in the generated image.

**Improve the display of data**
This is a broad term, but this time looking at the "most active roles" output in `/stats server` I would like to do a few things:

- Reorder the roles so it goes from most-contributed to least-contributed
- Make the y axis scale by some reasonable multiple (ideally multiples of 10)
- Subject to discussion, remove roles from the bar chart that contribute less than some proportion (say 5%) of server messages (or replacing it with an "other" option). This last suggestion should have the effect of making the chart far easier to read.