0032921: require minimum CMAKE version 3.1 (for enabling CMAKE_CXX_STANDARD)

0032921: require minimum CMAKE version 3.1 (for enabling CMAKE_CXX_STANDARD)

If we require CMAKE minimal version 3.1, rather than 2.8,
by default new policies are employed:
from CMP0024 to CMP0054.
Unique problematic policy is CMP0054:
`Only interpret if() arguments as variables or keywords when unquoted.`

Requiring of 3.1 as minimal version without preserving old behavior of 54th policy breaks MSVC compilation.
If we require cmake_policy (SET CMP0054 OLD), compilation finishs without errors.
New behavior of CMP0054 leads to changes in next target MSVC vcxproj files:
 - TKV3d
 - TKOpenGl
 - TKOpenGlTest
 - TKOpenGles
 - TKOpenGlesTest
Difference is absense of HAVE_OPENGL/HAVE_OPENGLES definitions.
So, source of error has been localizedin file occt_toolkit.cmake, in lines ~325 and ~327.
In accordance with old CMP0054 policy "CSF_OpenGlLibs" interprets as variable CSF_OpenGlLibs, rather than just a string.
Contrary, new policy interpret "CSF_OpenGlLibs" as a string.
To employ new policy, began since CMAKE 3.1 we should replace "CSF_OpenGlLibs" to "${CSF_OpenGlLibs}"
and "CSF_OpenGlesLibs" to "${CSF_OpenGlesLibs}".

P.S.

When cmake policy CMP0054 is set to NEW
expression
  "${CURRENT_CSF}" STREQUAL "CSF_OpenGlLibs"
is false,
while if policy CMP0054 is set to OLD
expression
  "${CURRENT_CSF}" STREQUAL "CSF_OpenGlLibs"
is true.
If replace "CSF_OpenGlLibs" to "${CSF_OpenGlLibs}"
expression is true independent on CMP0054 policy.
Notice, that OLD policy had beed taken place by default on master before
this ticket integration.