Project restructuring in preparation for release

Overview

The following changes were made in preparation for a release (the x64 branch should drop soon):

Add support for building workshop content addon
Move generated source files into gen/ folder.
Generated source files now return a value that can be included, rather than directly modifying a reference on the speak table.
This means that the VGUI Paint functions have been moved into vgui/speak_chatbox.lua
Third party dependencies have been moved into the vendor/ folder.
Added log.lua to vendor/.
My own libraries / classes have been moved into the lib/ folder.
In an attempt to reduce the number of references created in the global namespace, convert classes/packages into Lua modules.
Relocate compatibility into speak/compat.
Remove Clockwork compatibility (will rewrite later).
Update DarkRP compatibility to satisfy linter.

See that the application builds and tests pass:

$ ./scripts/cibuild
 . . .