This removes a cyclical dependency when importing client/structs from
dependencies of the plugin_loader, specifically, drivers. Due to
client/config also depending on the plugin_loader.
It also better reflects the ownership of fingerprint structs, as they
are fairly internal to the fingerprint manager.
Allow to set the total memory of an agent in its configuration file. This
can be used in case the automatic detection doesn't work or in specific
environments when memory overcommit (using swap for example) can be
desirable.
