Adding showPreviousMonths property

[gyugyu]

This pull request adds showPreviousMonths property to show previous months when monthsShown is configured.

[codecov-io]

Codecov Report

Merging #1007 into master will increase coverage by 6.96%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1007      +/-   ##
==========================================
+ Coverage   78.77%   85.73%   +6.96%     
==========================================
  Files          13       12       -1     
  Lines         716      638      -78     
  Branches      141      129      -12     
==========================================
- Hits          564      547      -17     
+ Misses         61        6      -55     
+ Partials       91       85       -6

Impacted Files	Coverage Δ
src/calendar.jsx	87.85% <100%> (+2.25%)	⬆️
src/time.jsx
src/datepicker.jsx	92.09% <0%> (+2.14%)	⬆️
src/date_utils.js	100% <0%> (+20.33%)	⬆️

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[kblodget]

Can this functionality be added to the master branch?

[martijnrusschen]

Got some merge conflicts, but should be good to go when resolved.

[kblodget]

Is there any way this may be added soon. This would be a great help to the project I am working on. I am willing to help out to get this feature added.

[martijnrusschen]

@kblodget We're waiting on resolving the merge conflicts.

[martijnrusschen]

Closing due inactivity.