Redmine 2.1.x compatibility (js+time tracking)

Solution borrowed from https://github.com/warnat/redmine-21-issue-hot-buttons/
Fixed json escaping

Solution borrowed from: https://github.com/panicinc/issue_hot_buttons/commit/869942db1bb6024d88accef662d9b8b1f4d44174
Disable timetracker not working in Chrome 28 while tab is inactive
Chrome 28-29 time bug workaround

https://code.google.com/p/chromium/issues/detail?id=259680
Merge branch 'master' of github.com:futurecolors/redmine-issue-hot-buttons

# By Ilya Baryshev
# Via Ilya Baryshev
* 'master' of github.com:futurecolors/redmine-issue-hot-buttons:
  Chrome 28-29 time bug workaround
  Disable timetracker not working in Chrome 28 while tab is inactive
  Fixed json escaping
  Redmine 2.1.x compatibility (js+time tracking)

Conflicts:
	app/views/hot_buttons/_assets.html.erb
	app/views/hot_buttons/_settings.html.erb
	assets/javascripts/hot_buttons.js
	assets/javascripts/prototype.js
	assets/javascripts/settings.js