[mediawiki.Uri] Add overrideKeys option

[mediawiki.Uri] Add overrideKeys option
* The behavior of turning foo=bar&foo=quux&lorem=ipsum into "{ lorem: 'ipsum', foo: ['bar', 'quux'] }", has annoyed me several times. As it is in contrary with the way PHP works (PHP only makes numeral arrays if the key ends in '[]'). Adding in an option to make mw.Uri behave like that.
* We may wanna make that the default at some point, leaving default behavior unchanged for now.
* Converted 'strictMode' into 'options', kept backwards compatibility
* Fixed documentation comment for example (q1=0 -> "{ q1: '0'")
* Updated unit tests to account for this option.