Port existing CodeMirror features

[cldwalker]

There are a number of CodeMirror features that this plugin does not have. This issue serves as a meta-issue until these are knocked out. Some of these may be broken out into separate cards. If you care about one of these, make a pull request for it :) Will keep this list up to date:

• Search/replace with confirm (openDialog)
• Replace over a range (openDialog)
• Motions combined with search e.g. d/be (openDialog) - from Unable to delete/change by "searching" #10
  • We'll need to let c/ and d/ passthrough which doesn't seem possible yet
• Search history - needs to be reimplemented to use LT's dialog
• Expose available ex-commands e.g. :sort and :global
  • Iterate over commands and pipe to handleEx

Issues marked with openDialog require an interactive dialog. The current dialog does not handle that yet.