git-gui: Convert browser, console to "class" format

Now that we have a slightly easier method of working with per-widget
data we should make use of that technique in our browser and console
meta-widgets, as both have a decent amount of information that they
store on a per-widget basis and our current approach of handling
it is difficult to follow.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
diff --git a/git-gui.sh b/git-gui.sh
index 84a3b62..67f993a 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -1288,7 +1288,7 @@
 
 .mbar.repository add command \
 	-label {Browse Current Branch} \
-	-command {new_browser $current_branch}
+	-command {browser::new $current_branch}
 trace add variable current_branch write ".mbar.repository entryconf [.mbar.repository index last] -label \"Browse \$current_branch\" ;#"
 .mbar.repository add separator
 
@@ -1581,7 +1581,7 @@
 		exit 1
 	}
 	set current_branch [lindex $argv 0]
-	new_browser $current_branch
+	browser::new $current_branch
 	return
 }
 blame {