KeplerGO/lightkurve: Lightkurve v1.2.0

Lightkurve v1.2.0 includes the following changes: Added flux_unit and flux_quantity properties to the LightCurve class to enable users to keep track of a light curve's flux units. [#591] Changed the default behavior of LightCurve.plot() to use normalize=False, ie. plots now display a light curve in its intrinsic units by default. [#591] Added an optional unit argument to LightCurve.normalize() to make it convenient to obtain a relative light curve in percent (unit='percent'), parts per thousand (unit='ppt') or parts per million (unit='ppm'). [#591] Changed LombScarglePeriodogram.from_lightcurve() to not normalize the input light curve by default. [#591] Changed LightCurve.normalize() to emit a warning if the light curve appears to be zero-centered. [#589] Fixed an issue which caused the search functions to be incompatible with the latest version of astroquery (v0.3.10). [#598] Added support for performing mathematical operations involving LightCurve objects, e.g. two LightCurve objects can now be added together. [#532] Updated the online tutorials (https://docs.lightkurve.org/tutorials) to take all recent Lightkurve API changes into account. [#596