more informative raw_plot text labels

[jpdeleon]

https://github.com/hpparvi/MuSCAT2_transit_pipeline/blob/e4cb993f37bb40dbf4fc4d77d922f485bd263a36/muscat2ph/phdata.py#L305

I propose to have more informative text labels so apertures instead of aperture indexes are shown in the plot.

 def plot_raw(self, nstars, ylim=(0.85, 1.15), ncols=4):
        apertures = self._ds.aperture.data
        date = self.mjd[0].iso.split(' ')[0]
        nrows = int(ceil(nstars / ncols))
        fig, axs = subplots(nrows, ncols, figsize=self.figsize, sharex=True, sharey=True)
        nflux = self.flux / self.flux.median('mjd')
        aids = abs(nflux.diff('mjd')).median('mjd').argmin('aperture')
        for i,(ax,iapt) in enumerate(zip(axs.flat, aids[:nstars])):
            apt = apertures[iapt]
            ax.plot(self.mjd.value, nflux[:,i,iapt], 'k')
            ax.text(0.05, 0.05, 'star id={}\nr={} pix'.format(i,int(apt)), 
                    transform=ax.transAxes, color='b', size='large')
        setp(axs, ylim=ylim)
        sb.despine(fig)
        pl.suptitle(date, fontsize='large')
        fig.tight_layout()
        return fig

[hpparvi]

Fixed.