Refactoring of android_rules.xml file

This is a new CL because of merge conflict in the old one.
Naming changed to 'property.name' style for property names.
Property 'value' attributes changed to 'location' for props containing location.
Suffix '.dir' added to properties' names indicating directories.
'-description' prefix added to intermediate/internal targets.
'*.location' properties removed, as 'location' attribute should take care of
full paths, adding $basedir implicitly, so hopefully there is no need to
define them explicitly.
External property names (taken from other files or hardcoded somewhere)
stayed untouched in this CL.
Some minor improvements to comments in order to make them more consistent.