Split C++ plugins into shared objects

[wadetb]

The V8, VNC, and VLC plugins are massive and are currently compiled directly into libshellspace.so.

These should be compiled into separate plugin .so files, which are dynamically loaded by the core via a "load xxx.so" command.

They should also be unloadable, and this should cause all the resources they have created to be unregistered (I think).

This will improve iteration time on C++ plugins and the core, because the core is currently huge due to the presence of these relatively stable plugins.