Fix peek bug and updates and standardization of plot() function

This PR fixes issue #1067 and standardizes plotting (especially in light curves). Adds new lightcurve property called plot_types which allows each lightcurve to define however many different plots they want. `peek()` is now only implemented in lightcurve.py and just runs `plot()` for each plot type available. A preview of the results of this PR can be seen in this [ipython notebook](http://nbviewer.ipython.org/github/ehsteve/ipython-notebooks/blob/master/Testing%20Peek().ipynb).