[BUILD] do not warn about unused functions

- Wunused-function is a concept with very limited utility and it will
  warn about all files that include a header with static functions but
  does not use _all_ of them.
- for example: ITRAQLabeler.cpp includes MatrixUtils.h and uses the
  function convertOpenMSMatrix2EigenMatrixXd but does not use
  matrixIsIdentityMatrix -> a warning will be emitted about the unused
  matrixIsIdentityMatrix function.
[FIX] removed unused typedefs
[FIX] add static cast (no narrowing conversion)
[FIX] add DLLAPI to two functions

- these two explicit template initializations are only ever included in
  BaseModel.cpp and are thus part of the library. To be visible to the
  client, they need to be exported explicitly (they are used in
  CONCEPT/Factory.h)
[FIX] add DLLAPI to assignment operator

- since the assignment operator of ToolDescription is available through
  the API, it also needs to able to assign ToolExternalDetails which
  contains a MappingParam object.
[FIX] add DLLAPI to two functions
[BUILD] turn on -fvisibility=hidden for gcc
made SplineSpectrum::Navigator public (not usable otherwise); fix compile error (VS2013) due to missing include; fixed interface(names); fixed intendation
fixed segfault (>=0 issue)
hide default Ctor; add missing tests (no content)
fixed loop vars
error handling for faulty spectra; more cleanup and tests
[FIX,TEST] MRMRTNormalizer_test: Windows compatibility
[FIX] fixed uninitialized pointer warning
Merge pull request #836 from grosenberger/fix/mrmrtnormalizer_test

[FIX,TEST] MRMRTNormalizer_test: Windows compatibility
Merge pull request #838 from hendrikweisser/fix-misc

[FIX] fixed uninitialized pointer warning
Merge pull request #835 from cbielow/fix_splineSpectrum

Fix spline spectrum
Merge pull request #834 from hroest/fix/fixWerror

Fix/fix werror
[FIX] fix pyOpenMS test
Merge pull request #840 from hroest/fix/fixpytest

[FIX] fix pyOpenMS test