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!

SConstruct

@@ -266,6 +266,7 @@ if 'blenderlite' in B.targets:
     target_env_defs['WITH_BF_BOOLEAN'] = False
     target_env_defs['WITH_BF_REMESH'] = False
     target_env_defs['WITH_BF_PYTHON'] = False
+    target_env_defs['WITH_BF_IME'] = False
     target_env_defs['WITH_BF_3DMOUSE'] = False
     target_env_defs['WITH_BF_LIBMV'] = False
     target_env_defs['WITH_BF_FREESTYLE'] = False