Try to clean up asset folders for sample apps. (#128)

* Try to clean up asset folders for sample apps.

This removes the build step where we copy a subset of assets, and makes
it so that FilamentApp hands out a "root path" for assets. For now this
is determined based on the location of the executable. This allows
developers to launch samples from any CWD.

Closes #11

* Restore asset copy to build.

libs/utils/src/Path.cpp

@@ -131,6 +131,14 @@ Path Path::getParent() const {
     return getCanonicalPath(result);
 }
 
+Path Path::getAncestor(int n) const {
+    Path result = getParent();
+    while (n--) {
+        result = result.getParent();
+    }
+    return result;
+}
+
 std::string Path::getName() const {
     if (isEmpty()) return "";