Make Gesture more of a framework

I removed the `gesture.go` script and the `Makefile` from the project and replaced them with a script (`gesture/build_bot`) that takes a standard Gesture config file, sniffs it for plugins, and generates a `gesture.go` script with those plugins included.

The bot generator script is pretty primitive. It assumes that the only plugins the 'bot will use are listed in the configuration. It also assumes that they'll be named with their fully qualified package name.

For now, the script also only dumps output to `stdout`. Deal with it.