Linux: added project part for QtCreator.

Allows easily setup cocos2d on Linux in QtCreator IDE.
Enabled c++0x flag, use OpenAL audio backend by default.
issue #2305:remove unneeded comment
Share top level Makefile between emscripten, linux and nacl.

Remove the custom top level Makefile.emscripten and instead
add build-emscripten.sh which can be used like build-linux.sh
and build-nacl.sh.

Also, use the top level lib folder to store emscripten libs.
This brings it in line with the other make-based builds.
Fix emscripten build on linux

Remove the dependacy of the emscripten build on /Library/Fonts
(a darwin-only folder).  On non-darwin platforms we use the
ariel.tff that is part of TestCpp.
issue #2305: Using c++11 std::thread instead of pthread for HttpClient class.
issue #2305: Fixing a crash when error is triggered in WebSocket. Using std::lock_guard to replace lock and unlock manually.
issue #2305: Reverting to use lock and unlock for HttpClient.
issue #2305: Fixing a bug that passing wrong mutex parameter to "wait".
issue #2305: Using the old logic of "wait".
issue #2305: Sleep(50) on Win32, usleep(50000) on unix --> std::this_thread::sleep_for(std::chrono::milliseconds(50));
Merge pull request #3001 from dumganhar/iss2305-std-thread

issue #2305: Using c++11 std::thread instead of pthread for HttpClient class.
issue #2305: [Win32] Removing the third party library pthreadVCE2.
Merge pull request #3003 from dumganhar/iss2305-std-thread

issue #2305: [Win32] Removing the third party library pthreadVCE2.
Merge pull request #2703 from sergey-shambir/linux_qmake

close #2332: [Linux] Adding project part for QtCreator.
Update AUTHORS [ci skip]
Merge pull request #2998 from sbc100/emscripten_linux

closed #2333: 1) Share top level Makefile between emscripten, linux and nacl.
2) Remove the dependacy of the emscripten build on /Library/Fonts
(a darwin-only folder).  On non-darwin platforms we use the
ariel.tff that is part of TestCpp.
Update AUTHORS [ci skip]
issue #2305: Using std::thread instead of pthread for ScriptingCore.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into iss2305-replace-pthread