Array support in m_Get tag

In-Portal has [b]m_Get[/b] tag, that is allows to display data, that was passed from web-browser, like url parameter or form field value right on the template.
This can be easily achieved by [b]<inp2:m_Get name="url_param_name"/>[/b] tag.

However, when it comes to multi-dimensional data structures on forms, e.g. input name on a form is like "some_name[sub_key][another_key]", then m_Get tag fails to display this, because PHP converts these keys into arrays, that should be accessed differently.

Here is the patch for square bracket support in m_Get tag.