Add date formatting

[sho-luv]

I added a way to change the following date variables:

• assessment_start_date
• assessment_emd_date

The config.json now has a date_format variable that takes ISO 8601 formats:

https://apidock.com/ruby/DateTime/strftime

This could be extended to logging if wanted. My code is crude. I simply check to see if the variable have been set, and if they have been I modify them using strtime just before they are added to the document. Works well enough. It also shouldn't mess with anything since I only change the date before it is entered into the word document. However, I could see a situation where someone messes up the ISO date format or adds special chars that cause the word doc to break down. I had a specif need and wrote this to scratch it. It might not meet all the needs. I am only making a pull request to share in what I did.

[jakxx]

Nice! Unless im missing something, this would take care of #467

Cheers @sho-luv !