Everything what was in src/ is now in src/Corrade, everything from
src/Plugins is now in src/MagnumPlugins, everything from external/ is in
src/MagnumExternal. Added new CMakeLists.txt file and updated the other
ones for the moves, no other change was made. If MAGNUM_BUILD_DEPRECATED
is set, everything compiles and installs like previously except for the
plugins, which are now in MagnumPlugins and not in Magnum/Plugins.
Some change in recent GCC (4.7.2) caused this to fail building, now
using duration_cast<microseconds>() instead of microseconds(). Also
cleaned up the code by importing std::duration prefix.
Optimalizations in Corrade::TestSuite and Corrade::Utility::Debug leaded
to significant reduction of compilation time - on my machine it was
~5:38 before with building of unit tests enabled, now only ~5:00.