plugins: change abstract plugin interface

This commit change the common plugin interface, in order for plugins
to be stoppable and customizable.

Signed-off-by: Luca Bruno <lucab@debian.org>
plugins: fix MemoryRangeIdentifier

Signed-off-by: Luca Bruno <lucab@debian.org>
Merge pull request #2 from lucab/lucab/plugins-iface

Plugin rework