added code to run the suites of the current (window) project, added plugin configuration, small refactor

I added some conveniences for the plugin

1. Now tests_dir is configurable globally and per project. As side effect of this, I renamed the UnitTesting.sublime-settings file that stores the recent packages to UnitTesting.recently-used that has more sense
2. There is now six commands available in the `Command Palette` (and they are prefixed with "UnitTesting")
    * UnitTesting: Run any project test suite
    * UnitTesting: Run any project test suite (Async)
    * UnitTesting: Run any project test suite (Deferred)
    * UnitTesting: Run current project test suite
    * UnitTesting: Run current project test suite (Async)
    * UnitTesting: Run current project test suite (Deferred)

All the **current project** versions take the name of the project from the currently opened project, if a name can't be infered, it just asks for the project name as the other versions of the command call

I just feel like project name, test_dir or etc should be window related properties rather than a view related properties. I am trying to avoid the use of view.
For the project settings, we can use `sublime.active_window().project_data().get("settings")`.