make utm and matplotlib optional

[jcapriot]

Makes utm and matplotlib optional dependencies for geoana.

• utm was being used in the earthquake module,
• matplotlib was being used in the earthquake and plotting_utils modules.

[codecov[bot]]

Codecov Report

Merging #64 (ab42295) into main (09e61cb) will decrease coverage by 0.25%. The diff coverage is 68.57%.

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
- Coverage   87.80%   87.56%   -0.25%     
==========================================
  Files          29       29              
  Lines        3009     3039      +30     
==========================================
+ Hits         2642     2661      +19     
- Misses        367      378      +11     

Impacted Files	Coverage Δ
geoana/utils.py	90.56% <61.53%> (-9.44%)	:arrow_down:
geoana/earthquake/oksar.py	56.52% <71.42%> (+0.15%)	:arrow_up:
geoana/plotting_utils.py	96.42% <75.00%> (-1.71%)	:arrow_down: