Backsync server->client communications made threadsafe

It used to be that on_open / on_close / on_message could be called while a post_save / post_delete was in progress. This could lead to the listeners array being modified while being iterated over (resulting in an exception), or two threads performing send() on the same connection at the same time (potentially resulting in corrupt messages). Introduced locks which prevent these two problems.
Creation of javascript objects moved out from FileStash.js & SendorTasks.js to a separate file, to make unit testing simpler
Added Jasmine 2.0.0 for unit testing
Added Sinon 1.7.3 for unit testing
Created unit tests and a simple spec runner for all models and SendorTasks view.

The testsuite is not comprehensive. The tests are set up to be run in a browser (no commandline invocation possible). It seems like it would be worth more to create functional tests (with a fake server on the client side, or against the real server?)
Introducing jasmine-jquery for DOM related unittests

Jasmine-jquery v1.7.0 is the latest official release but it is not compatible with Jasmine 2.x yet. Therefore a dev branch is also introduced (and that is what we will use until further notice).
Targets view is now a proper subview of StashedFileView; created some DOM-related JS unittests
Frontend tests can be run from the commandline using PhantomJS; makefile for frontend+backend tests

The backend testsuite prints a fair bit of irrelevant info to stdout. Should clean that up to make the results easier to interpret.