Better default TPF stretch

[bmorris3]

This PR gives a better default colormap stretch on TPF files. It sets vmin/vmax to the 5/99 percentile limits from the cube:

from lightkurve import search_targetpixelfile, search_lightcurve
from lcviz import LCviz

target = 'TRAPPIST-1'
lc = search_lightcurve(target, mission="K2", cadence="long").download().normalize()
tpf = search_targetpixelfile(target, mission="K2", cadence="long").download()

# Load the light curve into LCviz:
lcviz = LCviz()
lcviz.load_data(lc)
lcviz.load_data(tpf)
lcviz.show()

viewer = lcviz.app.get_viewer('flux-vs-time')
viewer.state.y_min = 0.9
viewer.state.y_max = 1.2

I opted to put this stretch as a private method in PlotOptions, and call the method from the parser when a TPF is loaded. That keeps the diff small. Caveats: this approach won't work if we load more than one TPF into the image viewer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.89%. Comparing base (7b78df5) to head (df51b0d).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
- Coverage   93.92%   91.89%   -2.04%     
==========================================
  Files          37       41       +4     
  Lines        1598     2012     +414     
==========================================
+ Hits         1501     1849     +348     
- Misses         97      163      +66     

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[kecnry]

I opted to put this stretch as a private method in PlotOptions, and call the method from the parser when a TPF is loaded. That keeps the diff small. Caveats: this approach won't work if we load more than one TPF into the image viewer.

What if we listened to adding new data or layers (either here or in the helper... but I would prefer in the plugin I think to keep the code in one place)?

[kecnry]

Thanks!!