sharing fixes plus enable editCode sharing [finishes #81962242]

* Enabled sharing for editCode levels by uploading the JavaScript program up to the service
* Enabled startBlocks for editCode levels (required to enable the above)
* Added freePlay to all webapp levels, added turtle level ec_1_10 and included it as /editcode/7 to test a freePlay editCode turtle level
* Replaced startBlocks on turtle ec_ levels with JavaScript equivalent code (required to replace the Blockly XML that was already there as a result of using utils.extend on existing Blockly levels)
* Fixed Pivotal Item 81962242. When I enabled re-sharing of shared levels back in June with this PR: https://github.com/code-dot-org/blockly/pull/676 , I should have preserved the old behavior when hide_source was turned on. Now that is fixed.
* Fixed margins on some parts of the visualization column in sharing mode. These seem to have gotten out-of-sync after the responsive layout changes this summer.
* Modified webapp to hide the Pause/Continue button and the speed slider if BlocklyApps.hideSource is true. Since these are essentially for debugging, it doesn't make sense to show them when you are looking at someone else's creation.