Panel tshift 4853
closes https://github.com/pydata/pandas/issues/4853

I think I'm doing this right. I moved the `tshift` into generic and had `shift` offload to `tshift` if `freq` is found. 

err, let me get Travis CI running on my fork. it passes nosetests on my local.
 - travis (I see you already started that!)
- release notes
 quick q, for the commits that make up a PR, do they need to follow the ENH/BUG/etc format? Or does everything get smushed into a single commit anyways when merged into master. 
 if u r going to squash then try to make the top one be descriptive
i try to make them all though
 You'll want to squash your commits down to a single commit before it's merged.

```
git fetch upstream
git checkout panel-tshift-4853
git rebase -i upstream/master
```

This should open your editor (`-i` stands for interactive) and you can follow the instructions there to squash or fixup your commits to just one.  Looking at your commits, you could probably squash the second into the first and then choose fixup for the other two.

Once that's done you can use `git push origin panel-tshift-4853 -f` to push to the branch in this PR.  Be careful with the `-f` option though.  This will mess things up if others are working off your branch.
 Does this change Series, DataFrame or any sparse object behavior? (given
that you're changing NDFrame) If so, should test.
 @dalejung I did a PR on your branch, https://github.com/dalejung/pandas/pull/1 which removes `shift` from series and dataframe and puts it in generic.py you can cherry-pick this.
 @jreback cherry picked the cleanup, added release notes, and enabled travis
 great looks good
will review soon
 err, sorry hold off a bit. I started generalizing the shift infrastructure so Panel could use it. Need to split off into its own branch
 okay, split off the additional work into its own branch/issue.
 @dalejung let me know if you want to merge this (or finish the other PR first)
 @jreback This can be merged first. thx
 alright..looks fine...can you squash down a bit?
 squashed. sorry used to hg where the commits don't carry over after merge. This PR has definitely leveled up my git-fu.
 thanks!
