Add an interface for handlers, rework the manager to always use
the interface instead of doing dodgy exported stuff.

Define a 'plugin' function to use in place of 'project' that
will figure out where the plugin is living in the root gradle
project.

This allows the plugins to be included and built properly
when they are in a submodule of either the client or the meta
project.

Change-Id: Iacc3551ac9c0bf2343151eb9cf85296c85c5a28b
Reviewed-on: http://gerrit.dmdirc.com/4028
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>

* Move all plugins to their own top-level directories.
* Move resources out of source trees
* Add Gradle build scripts.
* Remove ivy and ant build scripts.

Change-Id: Ib69a48ef26800c174ccf51c84ff9d1f73529460f
Depends-On: I303b6b69518468f98d48d835b8f40135d9e4bcbf
Reviewed-on: http://gerrit.dmdirc.com/3850
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>