Apps - make ANT building easier is a already built tree

Gradle apps - does the right thing but we should be able to rebuild easier.

Adding this bit of magic will allow for standalone rebuilds:

    <target name="-pre-init">
        <condition property="osname" value="win">
            <os family="windows"/>
        </condition>
        <condition property="osname" value="mac">
            <os family="mac"/>
        </condition>
        <condition property="osname" value="linux">
            <os name="linux"/>
        </condition>

        <property name="jfxbuild.jfxrt.jar" value="../../../build/${osname}-sdk/rt/lib/ext/jfxrt.jar"/>
    </target>