Added parsing of exptime and period from master files (#256)

- New aare:to_string/string_to similar to what we have in
slsDetectorPackage
- Added members period and exptime to RawMasterFile
- Parsing exposure time and period for json and raw master file formats
- Parsing of RawMasterFile from string stream to enable test without
files

Comments:

- to_string is at the moment not a public header. Can make it later if
needed. This gives us full freedom with the API
- FileConfig should probably be deprecated need to look into it.
Meanwhile removed python bindings and string conv

CMakeLists.txt

@@ -387,6 +387,7 @@ set(SourceFiles
     ${CMAKE_CURRENT_SOURCE_DIR}/src/RawFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/RawMasterFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/RawSubFile.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/to_string.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/utils/task.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/utils/ifstream_helpers.cpp
 ) 
@@ -460,6 +461,7 @@ if(AARE_TESTS)
             ${CMAKE_CURRENT_SOURCE_DIR}/src/RawFile.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/RawSubFile.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/utils/task.test.cpp
+            ${CMAKE_CURRENT_SOURCE_DIR}/src/to_string.test.cpp
 
         )
     target_sources(tests PRIVATE ${TestSources} )