Rename activity option

[lowtower]

This PR renames the option "activity" to "activity_type" to be more clear and consistent with other options.
Additionally, this PR adds the filter "--activity-type" and other options to the README by running the script update-readme.

[flopp]

This could break some existing installations - maybe we should add an alias to be backwards compatible...

[flopp]

args_parser.add_argument(["--activity-type", "--activity"], ...) should work, I guess.

[lowtower]

To be honest, my initial PR was committed maybe a bit hastily.
With this PR, I want to correct some (in my eyes) messy inconsistencies, which is rather cosmetic than really necessary.
You are right, that this would break existing installations.
It's Your tool - You decide which way to go.
I am fine with both names as options (pushed with commit f27d93e)

[flopp]

Thank you!