Fix ComponentTranslation encoding on non-UTF-8-by-default platforms

Javac default output format for files is platform-specific. In the
ai.apt macro we do not specify the encoding, so we end up with
ISO-8859-1 strings on Windows that GWT later attempts to decode as
UTF-8 strings. This commit sets the encoding for the javac command to
be UTF-8 so that encodings work correctly on platforms (e.g., Windows)
where the default encoding is not UTF-8.

Change-Id: Iac68786e71983e8605e982a093d3daae09d49c01

appinventor/components/build.xml

@@ -225,6 +225,7 @@
         </fileset>
       </delete>
       <javac destdir="@{apt-classdir}"
+             encoding="utf-8"
              sourcepath=""
              srcdir="${src.dir}"
              includeantruntime="false">