Add setting for limiting how many historical messages to fetch from the recent-messages api

[pajlada]

What should be added?
The ability to limit how many messages are fetched for each channel from the Recent Messages API. This can be achieved by passing the ?limit query parameter to the recent messages API.

Why should it be added?
Performance - in case your computer doesn't like you fetching up-to 800 messages (the default) from the API.

API Docs: https://recent-messages.robotty.de/api