Don't overwrite bot_core_lcmtypes

[patmarion]

I think that most users of this repo are also using bot_core_lcmtypes. This can result in a bug if the lcmtypes from this project are installed over the those from bot_core_lcmtypes.

As a quick fix to avoid this bug, I propose that we add a CMake flag, SKIP_BOTCORE_LCMTYPES, which causes this repo to use the installed types from bot_core_lcmtypes and entirely skip over processing the core types in this project, libbot.

This bug has currently manifested itself in drake's install tree on Mac OSX: bot_core_lcmtypes are installed into the site-packages, while libbot's bot2-core/lcmtypes are installed to dist-packages. Ouch!

[jamiesnape]

This repository is deprecated. Please contribute to the upstream https://github.com/libbot2/libbot2 or the new fork https://github.com/RobotLocomotion/libbot2 instead.