Default the plotting unit to None

[xiki-tempula]

Fix #247 Default the unit in plot_dF_state , plot_convergence and plot_ti_dhdl to None. Remove the array input in plot_convergence.

I have fixed the issue here @DrDomenicoMarson

[codecov[bot]]

Codecov Report

Merging #260 (67400a5) into master (316f228) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #260   +/-   ##
=======================================
  Coverage   98.65%   98.65%           
=======================================
  Files          26       26           
  Lines        1709     1711    +2     
  Branches      350      352    +2     
=======================================
+ Hits         1686     1688    +2     
  Misses          3        3           
  Partials       20       20           

Impacted Files	Coverage Δ
src/alchemlyb/visualisation/convergence.py	100.00% <100.00%> (ø)
src/alchemlyb/visualisation/dF_state.py	95.83% <100.00%> (+0.07%)	:arrow_up:
src/alchemlyb/visualisation/ti_dhdl.py	100.00% <100.00%> (ø)

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[xiki-tempula]

@orbeckst Thanks for the review. I have added the change log

Is there a test that shows that (1) None works and that (2) changing units works?

I have added this as well.

[orbeckst]

thanks!