Add fied time and date merge tags modifier

[omarkasem]

This implements #2040.

• I created merge tags modifier 'format' for both time and date
• The only thing that is not clear to me is when does this hook run gravityview/merge_tags/modifiers/value I tried a lot of values and modifiers but I can't get it to run so i can see if it has anything to do with date or time {Time:4:format:g:i a} {Date:3:format:m-d-Y}

💾 Build file (a2f040155).