Add Console for live query of Page/Site data

Query console supports searching and viewing page relations, page variables
and site variables.

pageexp[:field|depoperator]

_pageexp_ and _field_ values are handled as Regular Expression and matched
against page.output_path and page[*] variables.

'site' is handled as a special pageexp and can be used to search for values
on the site object.

_depoperator_ can have the value > to list the pages that the page
that match the _pageexp_ depend on, or < to list the dependents.

Example:

$> page1:<

page1
 < page2

$> page1:title

page1
  title -> 'X'

Activate console by using cli option --console

Issue: #211