Making Processing-Templates fit for Git

**Problem**

When several people work on a Processing library or tool via git, they usually have different classpaths, sketchbook locations etc. These things are configured in a file that is currently under version control (which is a bad thing).

**Solution**

 * Create custom config files named `local.properties` that are excluded from version control.
 * Provide template files: `local.properties.tmpl` that the developers need to copy and customize to their needs.
 * modify the build process to use both `local.properties` and `build.properties`