Hi,
Plugins are simple jar files in scm-manager 1.x, that means that they not ship their dependencies. If you want to introduce a new dependency you have to ship it by yourself.
But you should consider to go another way, which should be much more comfortable. For development you don't have to copy your plugin to /WEB-INF/lib, you can just run mvn scmp:run. The maven goal starts scm-manager an instance which has you plugin pre-installed. The only problem is that you are using a copy of an existing core plugin which leads to class conflicts. So you could refactor your plugin to avoid these class conflicts (rename the package).
But copying code is never a good way. I think the best way for getting read permissions in scm-manager is to introduce an api to the core of scm-manager which can be used in a plugin.
Sebastian