Read flavormap.properties as resource

After http://ccc.us.oracle.com/8005250 all but one references to flavormap.properties were removed from the documentation.
Under this bug the following work should be done:
1. Move flavor map.properties to resources, same as in JDK-8039362
2. Remove the remaining mention of the file from public documentation
3. Change format of the file. Currently we allow it to have duplicated keys. To support it we have 200+ lines of copy-pasted code in SystemFlavorMap. The format needs to be changed to use a comma as a separator in the list of flavors corresponding to a single native