make webserver stoppable once created

[kaduvert]

If the bot starting process includes creating a webserver you can't replay it because the default port is already bound and can't be freed this pr makes freeing possible by adding a stopServer() method

That's useful if you have to recreate your bot sometimes (possibly due to disconnects) but don't want to recreate the whole node process

[rom1504]

not sure on whether to merge more things like this here vs merging one of the massive PRs open

[kaduvert]

do both. the open prs don't conflict with each other except for maybe #175, but that's another project anyways..

[sefirosweb]

I need it, sometimes I check the bot to see how it is, but I could launch a task if there is no open connection that automatically stops the service, to improve performance/consumption