Add a status bar to the CodeEditor

- Show counts of errors/warnings/info annotations. This is useful
  because the annotations are in the gutter, so in big files it takes
  a lot of scrolling to look for errors
- Clicking the totals count skips you to the 'next' annotation
- If the current line contains an error, show the message of the error
  in the status bar.
- Show the current line:column number, the selection range and the
  editor mode.
- Degrades to a useful and readable but not pretty state in IE7

More complex version of: Ib9f08fcbc0365302756095b9027289736856fc73

Bug: 63294
Change-Id: Ided0804d5eb7864452287087dd1cf5a3dd8ff078
Merge "Add a status bar to the CodeEditor"