Add `other-buffer` flag to `cider-jump-to`
Don't forget offset line in `cider-stacktrace-navigate`.
Fix `cider-jump-to-var` with no symbol at point

  Also, make `cider-jump-to-var` and `cider-stacktrace-navigate` use common
  workhorse.
Merge pull request #761 from vitoshka/jump-to-var

`cider-jump-to-var` is broken when there is no symbol at point