Bug 731074 - console.log not working from a panel's script

- Added web console methods to plain-text console
- Added plain-text console to web pages in documents not in a tab
- Updated unit test
Addressed review's comment and suggestion.
Merge pull request #722 from ZER0/panel-console/731074

Fix Bug 731074 - console.log not working from a panel's script r=@Gozala, @ochameau