Remove deprecated plotting options

[dnerini]

This PR introduces two main changes in the visualization module and its tests, namely:

• Mock pyplot.show during tests to avoid opening interactive windows
• Apply pre-warned deprecation of keyword arguments for v1.6 (see below).

Deprecated arguments

concerns keyword arguments to:

• visualization.animations.animate()
• visualization.precipfields.plot_precip_field()

Must be passed to precip_kwargs instead:

• units
• colorbar
• colorscale

Renamed:

• type -> ptype
• timestamps -> timestamps_obs
• plotanimation-> display_animation

[codecov[bot]]

Codecov Report

Merging #266 (32dddfe) into master (72f3bf5) will increase coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #266      +/-   ##
==========================================
+ Coverage   80.92%   80.98%   +0.05%     
==========================================
  Files         142      142              
  Lines       10758    10739      -19     
==========================================
- Hits         8706     8697       -9     
+ Misses       2052     2042      -10     

Flag	Coverage Δ
unit_tests	80.98% <100.00%> (+0.05%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pysteps/visualization/animations.py	92.92% <ø> (+6.20%)	:arrow_up:
pysteps/visualization/precipfields.py	83.84% <ø> (+1.13%)	:arrow_up:
pysteps/tests/test_plt_animate.py	100.00% <100.00%> (ø)

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