Move js files into src/

Test plan:
- Make sure huxley tests, jasmine tests, make build, make metrics, make test all
  still work.

Auditors: alpert

metrics/replace_line.py

@@ -2,12 +2,12 @@
 
 import sys
 
-with open("../fontMetrics.js", "r") as metrics:
+with open("../src/fontMetrics.js", "r") as metrics:
     old_lines = file.readlines(metrics)
 
 replace = sys.stdin.read()
 
-with open("../fontMetrics.js", "w") as output:
+with open("../src/fontMetrics.js", "w") as output:
     for line in old_lines:
         if line.startswith("var metricMap"):
             output.write("var metricMap = ")