vnstat expose MonthRotate in UI

[gpfountz]

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Describe the problem

Expose the MonthRotate config file parameter to allow rotating the monthly log on a day other than the first of the month. In my example, my ISP has data caps that reset on the 14th of the month.

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Describe the proposed solution

Modify the config model to pull in the MonthRotate parameter and expose this setting on the General page.

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Related issue

If this pull request relates to an issue, link it here.
#5482

[mimugmail]

Please also update the version in Makefile

[gpfountz]

Please also update the version in Makefile

version in makefile updated -- Commit 530247c. Thanks for all your help!