The JavaScript console can be opened with Control+I, or using
the menu option. The console is currently a text box with JS
syntax highlighting which will send commands to the document's
interpreter. All output is printed to an HTML view in the console.
The output is an HtmlView to easily allow complex output, such
as expandable views for JS Objects in the long run.
Note that this is a little bit unreliable with the keyboard shortcut
since LibGUI can get confused about which Action it's supposed to use
as each Browser::Tab has its own "close tab" action. This will need
to be fixed in LibGUI.
This patch moves most of the Browser UI into a Tab class. The main UI
now mainly consists of a GUI::TabWidget that Tab objects are added to.
I'm going with the "tabs on top" style here, since I like how it makes
it feel like each tab has its own UI controls (which it actually does!)
