Input Method Editor (IME) support for text buttons

Original patch by @random (D765) with some minor work done by @campbell
and me.

At this place, I'd like call out a number of people who were involved and
deserve a big "Thank you!":
* At the first place @randon who developed and submitted the patch
* The Blendercn community which helped a lot with testing - espacially
* @yuzukyo, @leon_cheung and @kjym3
* @campbellbarton, @mont29 and @sergey for their help and advises during
* review
* @ton who realized the importance of this early on and asked me for
* reviewing

We are still not finished, as this is only the first part of the
implementaion, but there's more to come!

CMakeLists.txt

@@ -318,6 +318,9 @@ mark_as_advanced(WITH_LIBMV_SCHUR_SPECIALIZATIONS)
 option(WITH_FREESTYLE     "Enable Freestyle (advanced edges rendering)" ON)
 
 # Misc
+if(WIN32)
+	option(WITH_INPUT_IME "Enable Input Method Editor (IME) for complex Asian character input" ON)
+endif()
 option(WITH_INPUT_NDOF "Enable NDOF input devices (SpaceNavigator and friends)" ${_init_INPUT_NDOF})
 option(WITH_RAYOPTIMIZATION	"Enable use of SIMD (SSE) optimizations for the raytracer" ON)
 option(WITH_OPENNL        "Enable use of Open Numerical Library" ON)
@@ -1151,6 +1154,10 @@ elseif(WIN32)
 
 		list(APPEND PLATFORM_LINKLIBS ws2_32 vfw32 winmm kernel32 user32 gdi32 comdlg32 advapi32 shfolder shell32 ole32 oleaut32 uuid psapi)
 
+		if(WITH_INPUT_IME)
+			list(APPEND PLATFORM_LINKLIBS imm32)
+		endif()
+
 		add_definitions(
 			-D_CRT_NONSTDC_NO_DEPRECATE
 			-D_CRT_SECURE_NO_DEPRECATE
@@ -1506,6 +1513,11 @@ elseif(WIN32)
 		endif()
 		
 		list(APPEND PLATFORM_LINKLIBS -lshell32 -lshfolder -lgdi32 -lmsvcrt -lwinmm -lmingw32 -lm -lws2_32 -lz -lstdc++ -lole32 -luuid -lwsock32 -lpsapi)
+
+		if(WITH_INPUT_IME)
+			list(APPEND PLATFORM_LINKLIBS -limm32)
+		endif()
+
 		set(PLATFORM_CFLAGS "-pipe -funsigned-char -fno-strict-aliasing")
 
 		if(WITH_MINGW64)