Manual update.
Deleted files not needed for zip file generation.
Added missing Apps.* keys related to the index page to prevent English
from being displayed.  In most cases, the messages were the empty string,
but for Apps.choiceIntro, I used machine-translated "Welcome to Blockly!".
Modified index/template.soy so the index offers all languages for which
Puzzle and Maze have been translated and so Turtle and Code only show up
if available in that language.

This commit does not include regeneration of the *.js files.
Files auto-generated from previous two commits.
Made major changes to script, including improving abstraction, and
re-generated blockly.zip.