views module: make variables lowercase (convention)

[willfurnass]

XDATA, YDATA and EIGENVALUES have been made lowercase as that's the convention for non-constants.

[willfurnass]

CI failing as this needs to be rebased on #380

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@3cd01ed). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master     #382   +/-   ##
=========================================
  Coverage          ?   11.42%           
=========================================
  Files             ?        9           
  Lines             ?     5787           
  Branches          ?     1582           
=========================================
  Hits              ?      661           
  Misses            ?     5100           
  Partials          ?       26

Impacted Files	Coverage Δ
mumot/views.py	8.82% <0%> (ø)

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