cmake missing some policies and min version

[cvvergara]

cmake needs some adjustments.

For 3.7 use policy (and eventually on 4.0 make the appropriate adjustments)

1. Change the cmake_minimum_required

CMake Deprecation Warning at CMakeLists.txt:1 (CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

2. Set the policy about boost

CMake Warning (dev) at CMakeLists.txt:89 (find_package):
  Policy CMP0167 is not set: The FindBoost module is removed.  Run "cmake
  --help-policy CMP0167" for policy details.  Use the cmake_policy command to
  set the policy and suppress this warning.

This warning is for project developers.  Use -Wno-dev to suppress it.

...

CMake Warning (dev) at CMakeLists.txt:95 (find_package):
  Policy CMP0144 is not set: find_package uses upper-case <PACKAGENAME>_ROOT
  variables.  Run "cmake --help-policy CMP0144" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  CMake variable BOOST_ROOT is set to:

    E:/jenkins/boost/rel-1_78_0w64gcc81

  For compatibility, find_package is ignoring the variable, but code in a
  .cmake module might still use it.

3. Set the policy about python and sphinx

CMake Warning (dev) at cmake/FindSphinx.cmake:46 (find_package):
  Policy CMP0148 is not set: The FindPythonInterp and FindPythonLibs modules
  are removed.  Run "cmake --help-policy CMP0148" for policy details.  Use
  the cmake_policy command to set the policy and suppress this warning.

Call Stack (most recent call first):
  doc/CMakeLists.txt:143 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.