Misc. Cleanup and upgrades

[Lusito]

• Removing unused panelmenu.js
• Adding alternative to the deprecated reparent method (see [Code cleanup] [1.8] Don't use deprecated "reparent" function #1131).
  • usage: global.reparentActor(actor, parent);
  • parent can be null.
  • does not care if actor already is a child of parent, so it can be removed and appended to the end by doing global.reparentActor(actor, actor.get_parent()).
• Refactoring log initialization out of the start method.
• Removed duplicate code snippet in dnd.js
• Error log cleanup, removes a lot of unnecessary output and fixes a bug with out of date extensions.
• get_num_instances_for_xlet moved to extension.js and renamed to get_max_instances

[Lusito]

@clefebvre: Can we get this into 1.8 ?
I guess I could make them separate pull requests if needed.

[clefebvre]

We can try, let's talk about it on the IRC.. or in the meeting if we don't meet before then.

[Lusito]

will be merged in separate pulls