Add files to devel package

The devel package was missing the protocol/mysql.h-file. Also,
added copyright and licence files and a devel-specific description.
The package target is now checked to be one of the recognized ones.

include/maxscale/CMakeLists.txt

@@ -23,3 +23,5 @@ file(GLOB GENERATD_HEADERS "${CMAKE_BINARY_DIR}/include/maxscale/*.hh")
 foreach(var ${GENERATD_HEADERS})
   install_header(${var} devel)
 endforeach()
+
+add_subdirectory(protocol)

include/maxscale/protocol/CMakeLists.txt

@@ -1,5 +1,5 @@
 file(GLOB HEADERS "*.h*")
 foreach(var ${HEADERS})
   get_filename_component(header ${var} NAME)
-  install_header(${header} devel)
+  install_custom_file(${header} ${CMAKE_INSTALL_INCLUDEDIR}/maxscale/protocol devel)
 endforeach()