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 don't think that is what the user expect at all. It was really bizarre for me the first time that I tried to use the plugin and I had to write the exact name of the project in the input line, the user expect to run the tests in the project that he is actually working o, or at least that is what I should expect.