It's kinda silly to have new() be generic when all it does is box the
objects anyway. It only makes code harder to write, as we cannot unify
the types to call Pipeline::new(), and instead we have to rely on
calling Pipeline::new() in the branches themselves.

It's not the biggest issue when we only have different formats, but at
some point we might want to add different aggregators as well (like a
sorting one or a counting one), so it would be bad if we suddenly had to
add all those branches.

This fix changes that, and we can build the pipeline piecewise by
having a Box<dyn Format> around, allowing us to combine it freely with
any Box<dyn Aggregator>.

Filtering based on guilds is slow, as it will have to retrieve every
guild name from the GW2 API, and it has to parse every log file instead
of bailing early.

Therefore, guilds are not searched by default, and have to be
explicitely turned on with --guilds.

In addition, this means that raidgrep will now need network access when
--guilds is passed, which was not the case before.