Wrong covers and/or metadata after automatic import

[bayang]

Jelu uses an external tool to automatically fetch metadata and covers online.
It seems, however, that results are becoming more and more irrelevant see #56 and #57.
After more investigations, it appears that the tool hits google and gets heavily rate limited.
So, its usage is still fine for one-off imports (like fetching the metadata for one book at a time on daily usage) but for the initial bulk import of your existing history, from goodreads for example, some covers or metadata will be wrong, it is still more useful than importing everything by hand though).

I will try to find alternatives to this, but in the meantime we will have to stick to that.
If it really bothers you, you can still turn off automatic metadata fetching before starting your import (there is a checkbox on the UI).

[bayang]

The recent v0.38.0 release is as first step towards getting rid of this problem.
We can now choose exactly which metadata plugins we want to use for a specific search and in which order to use them.
In the future we can have more specific or pertinent metadat grabbers for specific use cases.

[bayang]

A new metadata plugin has been added in 0.61.0 hopefully it will allow us to circumvent all the cases where the default calibre plugin gets rate limited.