Select properties

Allow the user to select system properties or environment variables to be added to the build.properties.
The user should be allowed to add the properties to one of the predefined sections like this:

<properties>
<property>
<name>user.home</name>
<section>build.runtime</section>
</property>
<property>
<name>unknown</name>
<section>build.java</section>
</property>
<property>
<name>file.separator</name>
<section>build.xxx</section>
</property>
<property>
<name>java.vendor.url</name>
<section>build.java</section>
</property>
</properties>
</configuration>

The fact that a property is unknown must be silently ignored. If a section is unknown, the property will be added to the build.misc section.