This installs UHDPython.cmake to lib/uhd/, so that OOT RFNoC modules can
use it (and don't have to use a version that ships with the OOT). This
makes maintanance of that file a lot easier.
Now that this file can (and should) be used outside of UHD, we
"namespace" the macros and functions by prefacing them with 'UHD_'
(e.g., there's now UHD_PYTHON_CHECK_MODULE).
This file requires creating UHDMinDepVersions.cmake, which also gets
installed.
This change adds the extension framwork that enables external libraries
to extend the UHD functionality in MultiUSRP and RFNoC. Its main purpose
is to be able to use external frontend modules, signal conditioning
modules etc. and to control them together with the USRP device. To make
it easier to install into the correct directory the UHD_MODULE_PATH gets
exported in CMake.
