FakeVim: Monitor inserted text using signals from QTextDocument

Use QTextDocument::onContentsChanged() to monitor text inserted and
removed in insert mode for dot command (or just repeat with 2i, 3o etc.)
to re-insert same text.

Works even if auto-completion is replacing '.' with '->' for pointers.

Change-Id: Ie39edcdc9ec60bcf6c7d10f021248c3a0aee76b6
Reviewed-by: hjk <hjk121@nokiamail.com>